Patent Application
20080274526
The invention relates to a method for the production of isobutanol by fermentation using a recombinant microbial host. Specifically, the method employs a decrease in temperature during fermentation that results in more robust tolerance of the production host to the isobutanol product.
Butanol is an important industrial chemical, useful as a fuel additive, as a feedstock chemical in the plastics industry, and as a foodgrade extractant in the food and flavor industry. Each year 10 to 12 billion pounds of butanol are produced by petrochemical means and the need for this commodity chemical will likely increase.
Methods for the chemical synthesis of isobutanol are known, such as oxo synthesis, catalytic hydrogenation of carbon monoxide (Ullmann's Encyclopedia of Industrial Chemistry, 6th edition, 2003, Wiley-VCHVerlag GmbH and Co., Weinheim, Germany, Vol. 5, pp. 716-719) and Guerbet condensation of methanol with n-propanol (Carlini et al., J. Mol. Catal. A:Chem. 220:215-220 (2004)). These processes use starting materials derived from petrochemicals and are generally expensive and are not environmentally friendly. The production of isobutanol from plant-derived raw materials would minimize greenhouse gas emissions and would represent an advance in the art.
Isobutanol is produced biologically as a by-product of yeast fermentation. It is a component of “fusel oil” that forms as a result of incomplete metabolism of amino acids by this group of fungi. Isobutanol is specifically produced from catabolism of L-valine. After the amine group of L-valine is harvested as a nitrogen source, the resulting α-keto acid is decarboxylated and reduced to isobutanol by enzymes of the so-called Ehrlich pathway (Dickinson et al., J. Biol. Chem. 273(40):25752-25756 (1998)). Yields of fusel oil and/or its components achieved during beverage fermentation are typically low. For example, the concentration of isobutanol produced in beer fermentation is reported to be less than 16 parts per million (Garcia et al., Process Biochemistry 29:303-309 (1994)). Addition of exogenous L-valine to the fermentation increases the yield of isobutanol, as described by Dickinson et al., supra, wherein it is reported that a yield of isobutanol of 3 g/L is obtained by providing L-valine at a concentration of 20 g/L in the fermentation. However, the use of valine as a feed-stock would be cost prohibitive for industrial scale isobutanol production. The biosynthesis of isobutanol directly from sugars would be economically viable and would represent an advance in the art.
Recombinant microbial production hosts expressing an isobutanol biosynthetic pathway have been described (Donaldson et al., copending and commonly owned U.S. Patent Application Publication No. US20070092957 A1). However, biological production of isobutanol is believed to be limited by butanol toxicity to the host microorganism used in the fermentation.
Some microbial strains that are tolerant to isobutanol are known in the art (Bramucci et al., copending and commonly owned U.S. patent application Ser. Nos. 11/743220 and 11/761,497). However, biological methods of producing isobutanol to higher levels are required for cost effective commercial production.
There have been reports describing the effect of temperature on the tolerance of some microbial strains to ethanol. For example, Amartey et al. (Biotechnol. Lett. 13(9):627-632 (1991)) disclose that Bacillus stearothermophillus is less tolerant to ethanol at 70° C. than at 60° C. Herrero et al. (Appl. Environ. Microbiol. 40(3):571-577 (1980)) report that the optimum growth temperature of a wild-type strain of Clostridium thermocellum decreases as the concentration of ethanol challenge increases, whereas the optimum growth temperature of an ethanol-tolerant mutant remains constant. Brown et al. (Biotechnol. Lett. 4(4):269-274 (1982)) disclose that the yeast Saccharomyces uvarum is more resistant to growth inhibition by ethanol at temperatures 5° C. and 10° C. below its growth optimum of 35° C. However, fermentation became more resistant to ethanol inhibition with increasing temperature. Additionally, Van Uden (CRC Crit. Rev. Biotechnol. 1(3):263-273 (1984)) report that ethanol and other alkanols depress the maximum and the optimum growth temperature for growth of Saccharomyces cerevisiae while thermal death is enhanced. Moreover, Lewis et al. (U.S. Patent Application Publication No. 2004/0234649) describe methods for producing high levels of ethanol during fermentation of plant material comprising decreasing the temperature during saccharifying, fermenting, or simultaneously saccharifying and fermenting.
Much less is known about the effect of temperature on the tolerance of microbial strains to butanols. Harada (Hakko Kyokaishi 20:155-156 (1962)) discloses that the yield of 1-butanol in acetone-butanol-ethanol (ABE) fermentation is increased from 18.4%-18.7% to 19.1%-21.2% by lowering the temperature from 30° C. to 28° C. when the growth of the bacteria reaches a maximum. Jones et al. (Microbiol. Rev. 50(4):484-524 (1986)) review the role of temperature in ABE fermentation. They report that the solvent yields of three different solvent producing strains remains fairly constant at 31% at 30° C. and 33° C., but decreases to 23 to 25% at 37° C. Similar results were reported for Clostridium acetobutylicum for which solvent yields decreased from 29% at 25° C. to 24% at 40° C. In the latter case, the decrease in solvent yield was attributed to a decrease in acetone production while the yield of 1-butanol was unaffected. However, Carnarius (U.S. Pat. No. 2,198,104) reports that an increase in the butanol ratio is obtained in the ABE process by decreasing the temperature of the fermentation from 30° C. to 24° C. after 16 hours. However, the effect of temperature on the production of isobutanol by recombinant microbial hosts is not known in the art.
There is a need, therefore, for a cost-effective process for the production of isobutanol by fermentation that provides higher yields than processes known in the art. The present invention addresses this need through the discovery of a method for producing isobutanol by fermentation using a recombinant microbial host, which employs a decrease in temperature during fermentation, resulting in more robust tolerance of the production host to the isobutanol product.
The invention provides a method for the production of isobutanol by fermentation using a recombinant microbial host, which employs a decrease in temperature during fermentation that results in more robust tolerance of the production host to the isobutanol product.
Accordingly, the invention provides a method for the production of isobutanol comprising:
The invention can be more fully understood from the following detailed description, figure, and the accompanying sequence descriptions, which form a part of this application.
The following sequences conform with 37 C.F.R. 1.821-1.825 (“Requirements for Patent Applications Containing Nucleotide Sequences and/or Amino Acid Sequence Disclosures—the Sequence Rules”) and are consistent with World Intellectual Property Organization (WIPO) Standard ST.25 (1998) and the sequence listing requirements of the EPO and PCT (Rules 5.2 and 49.5(a-bis), and Section 208 and Annex C of the Administrative Instructions). The symbols and format used for nucleotide and amino acid sequence data comply with the rules set forth in 37 C.F.R. §1.822.
Klebsiella pneumoniae budB
Bacillus subtilis alsS
Lactococcus lactis als
E. coli ilvC (acetohydroxy acid
S. cerevisiae ILV5
M. maripaludis ilvC
B. subtilis ilvC
E. coli ilvD (acetohydroxy acid
S. cerevisiae ILV3
M. maripaludis ilvD
B. subtilis ilvD
Lactococcus lactis kivD (branched-
Lactococcus lactis kivD (branched-
Lactococcus lactis kdcA
Salmonella typhimurium
Clostridium acetobutylicum pdc
E. coli yqhD (branched-chain alcohol
S. cerevisiae YPR1
S. cerevisiae ADH6
Clostridium acetobutylicum bdhA
Clostridium acetobutylicum bdhB
B. subtilis bkdAA
B. subtilis bkdAB
B. subtilis bkdB
B. subtilis lpdV
P. putida bkdA1
P. putida bkdA2
P. putida bkdB
P. putida 1pdV
C. beijerinckii ald
C. acetobutylicum adhe1
C. acetobutylicum adhe
P. putida nahO
T. thermophilus
E. coli avtA
B. licheniformis avtA
E. coli ilvE
S. cerevisiae BAT2
M. thermoautotrophicum
S. coelicolor
B.. subtilis bcd
S. viridifaciens
A. denitrificans aptA
R. eutropha
S. oneidensis
P. putida
S. cinnamonensis icm
S. cinnamonensis icmB
S. coelicolor SCO5415
S. coelicolor SCO4800
S. avermitilis icmA
S. avermitilis icmB
SEQ ID NOs:11-38, 40-69, 72-75, 85-138, 144, 145, 147-157, 159-176 are the nucleotide sequences of oligonucleotide cloning, screening or sequencing primers used in the Examples described herein.
SEQ ID NO:39 is the nucleotide sequence of the cscBKA gene cluster described in Example 20.
SEQ ID NO:70 is the nucleotide sequence of the glucose isomerase promoter 1.6GI described in Example 17.
SEQ ID NO:71 is the nucleotide sequence of the 1.5GI promoter described in Example 17.
SEQ ID NO:76 is the nucleotide sequence of the GPD promoter described in Example 21.
SEQ ID NO:77 is the nucleotide sequence of the CYC1 terminator described in Example 21.
SEQ ID NO:79 is the nucleotide sequence of the FBA promoter described in Example 21.
SEQ ID NO:81 is the nucleotide sequence of ADH1 promoter described in Example 21.
SEQ ID NO:82 is the nucleotide sequence of ADH1 terminator described in Example 21.
SEQ ID NO:84 is the nucleotide sequence of GPM promoter described in Example 21.
SEQ ID NO:139 is the amino acid sequence of sucrose hydrolase (CscA).
SEQ ID NO:140 is the amino acid sequence of D-fructokinase (CscK).
SEQ ID NO:141 is the amino acid sequence of sucrose permease (CscB).
SEQ ID NO:142 is the nucleotide sequence of plasmid pFP988DssPspac described in Example 24.
SEQ ID NO:143 is the nucleotide sequence of plasmid pFP988DssPgroE described in Example 24.
SEQ ID NO:146 is the nucleotide sequence of the pFP988Dss vector fragment described in Example 24.
SEQ ID NO:177 is the nucleotide sequence of the pFP988 integration vector described in Example 25.
SEQ ID NO:267 is the nucleotide sequence of plasmid pC194 described in Example 25.
The present invention relates to a method for the production of isobutanol using recombinant microorganisms that employs a decrease in temperature during fermentation, resulting in more robust tolerance of the production host to the isobutanol product and therefore a higher titer of isobutanol. The present invention meets a number of commercial and industrial needs. Butanol is an important industrial commodity chemical with a variety of applications, where its potential as a fuel or fuel additive is particularly significant. Although only a four-carbon alcohol, butanol has an energy content similar to that of gasoline and can be blended with any fossil fuel. Butanol is favored as a fuel or fuel additive as it yields only CO2 and little or no SOX or NOX when burned in the standard internal combustion engine. Additionally butanol is less corrosive than ethanol, the most preferred fuel additive to date.
In addition to its utility as a biofuel or fuel additive, butanol has the potential of impacting hydrogen distribution problems in the emerging fuel cell industry. Fuel cells today are plagued by safety concerns associated with hydrogen transport and distribution. Butanol can be easily reformed for its hydrogen content and can be distributed through existing gas stations in the purity required for either fuel cells or vehicles.
Finally the present invention produces isobutanol from plant derived carbon sources, avoiding the negative environmental impact associated with standard petrochemical processes for butanol production.
The following definitions and abbreviations are to be used for the interpretation of the claims and the specification.
As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” “contains” or “containing,” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).
Also, the indefinite articles “a” and “an” preceding an element or component of the invention are intended to be nonrestrictive regarding the number of instances (i.e. occurrences) of the element or component. Therefore “a” or “an” should be read to include one or at least one, and the singular word form of the element or component also includes the plural unless the number is obviously meant to be singular.
The term “invention” or “present invention” as used herein is a non-limiting term and is not intended to refer to any single embodiment of the particular invention but encompasses all possible embodiments as described in the specification and the claims.
As used herein, the term “about” modifying the quantity of an ingredient or reactant of the invention employed refers to variation in the numerical quantity that can occur, for example, through typical measuring and liquid handling procedures used for making concentrates or use solutions in the real world; through inadvertent error in these procedures; through differences in the manufacture, source, or purity of the ingredients employed to make the compositions or carry out the methods; and the like. The term “about” also encompasses amounts that differ due to different equilibrium conditions for a composition resulting from a particular initial mixture. Whether or not modified by the term “about”, the claims include equivalents to the quantities. In one embodiment, the term “about” means within 10% of the reported numerical value, preferably within 5% of the reported numerical value.
The term “isobutanol biosynthetic pathway” refers to an enzyme pathway to produce isobutanol.
The terms “acetolactate synthase” and “acetolactate synthetase” are used intechangeably herein to refer to an enzyme that catalyzes the conversion of pyruvate to acetolactate and CO2. Preferred acetolactate synthases are known by the EC number 2.2.1.69 (Enzyme Nomenclature 1992, Academic Press, San Diego). These enzymes are available from a number of sources, including, but not limited to, Bacillus subtilis (GenBank Nos: CAB15618 (SEQ ID NO:178), Z99122 (SEQ ID NO:78), NCBI (National Center for Biotechnology Information) amino acid sequence, NCBI nucleotide sequence, respectively), Klebsiella pneumoniae (GenBank Nos: AAA25079 (SEQ ID NO:2), M73842 (SEQ ID NO:1)), and Lactococcus lactis (GenBank Nos: AAA25161 (SEQ ID NO:180), L16975 (SEQ ID NO:179)).
The terms “acetohydroxy acid isomeroreductase” and “acetohydroxy acid reductoisomerase” are used interchangeably herein to refer to an enzyme that catalyzes the conversion of acetolactate to 2,3-dihydroxyisovalerate using NADPH (reduced nicotinamide adenine dinucleotide phosphate) as an electron donor. Preferred acetohydroxy acid isomeroreductases are known by the EC number 1.1.1.86 and sequences are available from a vast array of microorganisms, including, but not limited to, Escherichia coli (GenBank Nos: NP—418222 (SEQ ID NO:4), NC—000913 (SEQ ID NO:3)), Saccharomyces cerevisiae (GenBank Nos: NP—013459 (SEQ ID NO:181), NC—001144 (SEQ ID NO:80)), Methanococcus maripaludis (GenBank Nos: CAF30210 (SEQ ID NO:183), BX957220 (SEQ ID NO:182)), and Bacillus. subtilis (GenBank Nos: CAB14789 (SEQ ID NO:185), Z99118 (SEQ ID NO:184)).
The term “acetohydroxy acid dehydratase” refers to an enzyme that catalyzes the conversion of 2,3-dihydroxyisovalerate to α-ketoisovalerate. Preferred acetohydroxy acid dehydratases are known by the EC number 4.2.1.9. These enzymes are available from a vast array of microorganisms, including, but not limited to, E. coli (GenBank Nos: YP—026248 (SEQ ID NO:6), NC—000913 (SEQ ID NO:5)), S. cerevisiae (GenBank Nos: NP—012550 (SEQ ID NO:186), NC—001142 (SEQ ID NO:83)), M. maripaludis (GenBank Nos: CAF29874 (SEQ ID NO:188), BX957219 (SEQ ID NO:187)), and B. subtilis (GenBank Nos: CAB14105 (SEQ ID NO:190), Z99115 (SEQ ID NO:189)).
The term “branched-chain α-keto acid decarboxylase” refers to an enzyme that catalyzes the conversion of α-ketoisovalerate to isobutyraldehyde and CO2. Preferred branched-chain α-keto acid decarboxylases are known by the EC number 4.1.1.72 and are available from a number of sources, including, but not limited to, Lactococcus lactis (GenBank Nos: AAS49166 (SEQ ID NO:193), AY548760 (SEQ ID NO:192); CAG34226 (SEQ ID NO:8), AJ746364 (SEQ ID NO:191), Salmonella typhimurium (GenBank Nos: NP—461346 (SEQ ID NO:195), NC—003197 (SEQ ID NO:194)), and Clostridium acetobutylicum (GenBank Nos: NP—149189 (SEQ ID NO:197), NC—001988 (SEQ ID NO:196)).
The term “branched-chain alcohol dehydrogenase” refers to an enzyme that catalyzes the conversion of isobutyraldehyde to isobutanol. Preferred branched-chain alcohol dehydrogenases are known by the EC number 1.1.1.265, but may also be classified under other alcohol dehydrogenases (specifically, EC 1.1.1.1 or 1.1.1.2). These enzymes utilize NADH (reduced nicotinamide adenine dinucleotide) and/or NADPH as electron donor and are available from a number of sources, including, but not limited to, S. cerevisiae (GenBank Nos: NP—010656 (SEQ ID NO:199), NC—001136 (SEQ ID NO:198); NP—014051 (SEQ ID NO:201) NC—001145 (SEQ ID NO:200)), E. coli (GenBank Nos: NP—417-484 (SEQ ID NO:10), NC—000913 (SEQ ID NO:9)), and C. acetobutylicum (GenBank Nos: NP—349892 (SEQ ID NO:203), NC—003030 (SEQ ID NO:202); NP—349891 (SEQ ID NO:204), NC—003030 (SEQ ID NO:158)).
The term “branched-chain keto acid dehydrogenase” refers to an enzyme that catalyzes the conversion of α-ketoisovalerate to isobutyryl-CoA (isobutyryl-coenzyme A), using NAD+ (nicotinamide adenine dinucleotide) as electron acceptor. Preferred branched-chain keto acid dehydrogenases are known by the EC number 1.2.4.4. These branched-chain keto acid dehydrogenases are comprised of four subunits and sequences from all subunits are available from a vast array of microorganisms, including, but not limited to, B. subtilis (GenBank Nos: CAB14336 (SEQ ID NO:206), Z99116 (SEQ ID NO:205); CAB14335 (SEQ ID NO:208), Z99116 (SEQ ID NO:207); CAB14334 (SEQ ID NO:210), Z99116 (SEQ ID NO:209); and CAB14337 (SEQ ID NO:212), Z99116 (SEQ ID NO:211)) and Pseudomonas putida (GenBank Nos: AAA65614 (SEQ ID NO:214), M57613 (SEQ ID NO:213); AAA65615 (SEQ ID NO:216), M57613 (SEQ ID NO:215); AAA65617 (SEQ ID NO:218), M57613 (SEQ ID NO:217); and AAA65618 (SEQ ID NO:220), M57613 (SEQ ID NO:219)).
The term “acylating aldehyde dehydrogenase” refers to an enzyme that catalyzes the conversion of isobutyryl-CoA to isobutyraldehyde, using either NADH or NADPH as electron donor. Preferred acylating aldehyde dehydrogenases are known by the EC numbers 1.2.1.10 and 1.2.1.57. These enzymes are available from multiple sources, including, but not limited to, Clostridium beijerinckii (GenBank Nos: AAD31841 (SEQ ID NO:222), AF157306 (SEQ ID NO:221)), C. acetobutylicum (GenBank Nos: NP—149325 (SEQ ID NO:224), NC—001988 (SEQ ID NO:223); NP—149199 (SEQ ID NO:226), NC—001988 (SEQ ID NO:225)), P. putida (GenBank Nos: AAA89106 (SEQ ID NO:228), U13232 (SEQ ID NO:227)), and Thermus thermophilus (GenBank Nos: YP—145486 (SEQ ID NO:230), NC—006461 (SEQ ID NO:229)).
The term “transaminase” refers to an enzyme that catalyzes the conversion of α-ketoisovalerate to L-valine, using either alanine or glutamate as amine donor. Preferred transaminases are known by the EC numbers 2.6.1.42 and 2.6.1.66. These enzymes are available from a number of sources. Examples of sources for alanine-dependent enzymes include, but are not limited to, E. coli (GenBank Nos: YP—026231 (SEQ ID NO:232), NC—000913 (SEQ ID NO:231)) and Bacillus licheniformis (GenBank Nos: YP—093743 (SEQ ID NO:234), NC—006322 (SEQ ID NO:233)). Examples of sources for glutamate-dependent enzymes include, but are not limited to, E. coli (GenBank Nos: YP—026247 (SEQ ID NO:236), NC—000913 (SEQ ID NO:235)), S. cerevisiae (GenBank Nos: NP—012682 (SEQ ID NO:238), NC—001142 (SEQ ID NO:237)) and Methanobacterium thermoautotrophicum (GenBank Nos: NP—276546 (SEQ ID NO:240), NC—000916 (SEQ ID NO:239)).
The term “valine dehydrogenase” refers to an enzyme that catalyzes the conversion of α-ketoisovalerate to L-valine, using NAD(P)H as electron donor and ammonia as amine donor. Preferred valine dehydrogenases are known by the EC numbers 1.4.1.8 and 1.4.1.9 and are available from a number of sources, including, but not limited to, Streptomyces coelicolor (GenBank Nos: NP—628270 (SEQ ID NO:242), NC—003888 (SEQ ID NO:241)) and B. subtilis (GenBank Nos: CAB14339 (SEQ ID NO:244), Z99116 (SEQ ID NO:243)).
The term “valine decarboxylase” refers to an enzyme that catalyzes the conversion of L-valine to isobutylamine and CO2. Preferred valine decarboxylases are known by the EC number 4.1.1.14. These enzymes are found in Streptomycetes, such as for example, Streptomyces viridifaciens (GenBank Nos: AAN10242 (SEQ ID NO:246), AY116644 (SEQ ID NO:245)).
The term “omega transaminase” refers to an enzyme that catalyzes the conversion of isobutylamine to isobutyraldehyde using a suitable amino acid as amine donor. Preferred omega transaminases are known by the EC number 2.6.1.18 and are available from a number of sources, including, but not limited to, Alcaligenes denitrificans (AAP92672 (SEQ ID NO:248), AY330220 (SEQ ID NO:247)), Ralstonia eutropha (GenBank Nos: YP—294474 (SEQ ID NO:250), NC—007347 (SEQ ID NO:249)), Shewanella oneidensis (GenBank Nos: NP—719046 (SEQ ID NO:252), NC—004347 (SEQ ID NO:251)), and P. putida (GenBank Nos: AAN66223 (SEQ ID NO:254), AE016776 (SEQ ID NO:253)).
The term “isobutyryl-CoA mutase” refers to an enzyme that catalyzes the conversion of butyryl-CoA to isobutyryl-CoA. This enzyme uses coenzyme B12 as cofactor. Preferred isobutyryl-CoA mutases are known by the EC number 5.4.99.13. These enzymes are found in a number of Streptomycetes, including, but not limited to, Streptomyces cinnamonensis (GenBank Nos: AAC08713 (SEQ ID NO:256), U67612 (SEQ ID NO:255); CAB59633 (SEQ ID NO:258), AJ246005 (SEQ ID NO:257)), S. coelicolor (GenBank Nos: CAB70645 (SEQ ID NO:260), AL939123 (SEQ ID NO:259); CAB92663 (SEQ ID NO:262), AL939121 (SEQ ID NO:261)), and Streptomyces avermitilis (GenBank Nos: NP—824008 (SEQ ID NO:264), NC—003155 (SEQ ID NO:263); NP—824637 (SEQ ID NO:266), NC—003155 (SEQ ID NO:265)).
The term “a facultative anaerobe” refers to a microorganism that can grow in both aerobic and anaerobic environments.
The term “carbon substrate” or “fermentable carbon substrate” refers to a carbon source capable of being metabolized by host organisms disclosed herein and particularly carbon sources selected from the group consisting of monosaccharides, oligosaccharides, polysaccharides, and one-carbon substrates or mixtures thereof.
The term “gene” refers to a nucleic acid fragment that is capable of being expressed as a specific protein, optionally including regulatory sequences preceding (5′ non-coding sequences) and following (3′ non-coding sequences) the coding sequence. “Native gene” refers to a gene as found in nature with its own regulatory sequences. “Chimeric gene” refers to any gene that is not a native gene, comprising regulatory and coding sequences that are not found together in nature. Accordingly, a chimeric gene may comprise regulatory sequences and coding sequences that are derived from different sources, or regulatory sequences and coding sequences derived from the same source, but arranged in a manner different than that found in nature. “Endogenous gene” refers to a native gene in its natural location in the genome of an organism. A “foreign gene” or “heterologous gene” refers to a gene not normally found in the host organism, but that is introduced into the host organism by gene transfer. Foreign genes can comprise native genes inserted into a non-native organism, or chimeric genes. A “transgene” is a gene that has been introduced into the genome by a transformation procedure.
As used herein, an “isolated nucleic acid fragment” or “isolated nucleic acid molecule” or “genetic construct” will be used interchangeably and will mean a polymer of RNA or DNA that is single- or double-stranded, optionally containing synthetic, non-natural or altered nucleotide bases. An isolated nucleic acid fragment in the form of a polymer of DNA may be comprised of one or more segments of cDNA, genomic DNA or synthetic DNA.
A nucleic acid fragment is “hybridizable” to another nucleic acid fragment, such as a cDNA, genomic DNA, or RNA molecule, when a single-stranded form of the nucleic acid fragment can anneal to the other nucleic acid fragment under the appropriate conditions of temperature and solution ionic strength. Hybridization and washing conditions are well known and exemplified in Sambrook, J., Fritsch, E. F. and Maniatis, T. Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor Laboratory: Cold Spring Harbor, N.Y. (1989), particularly Chapter 11 and Table 11.1 therein (entirely incorporated herein by reference). The conditions of temperature and ionic strength determine the “stringency” of the hybridization. Stringency conditions can be adjusted to screen for moderately similar fragments (such as homologous sequences from distantly related organisms), to highly similar fragments (such as genes that duplicate functional enzymes from closely related organisms). Post-hybridization washes determine stringency conditions. One set of preferred conditions uses a series of washes starting with 6×SSC, 0.5% SDS at room temperature for 15 min, then repeated with 2×SSC, 0.5% SDS at 45° C. for 30 min, and then repeated twice with 0.2×SSC, 0.5% SDS at 50° C. for 30 min. A more preferred set of stringent conditions uses higher temperatures in which the washes are identical to those above except for the temperature of the final two 30 min washes in 0.2×SSC, 0.5% SDS was increased to 60° C. Another preferred set of highly stringent conditions uses two final washes in 0.1×SSC, 0.1% SDS at 65° C. An additional set of stringent conditions include hybridization at 0.1×SSC, 0.1% SDS, 65° C. and washes with 2×SSC, 0.1% SDS followed by 0.1×SSC, 0.1% SDS, for example.
Hybridization requires that the two nucleic acids contain complementary sequences, although depending on the stringency of the hybridization, mismatches between bases are possible. The appropriate stringency for hybridizing nucleic acids depends on the length of the nucleic acids and the degree of complementation, variables well known in the art. The greater the degree of similarity or homology between two nucleotide sequences, the greater the value of Tm for hybrids of nucleic acids having those sequences. The relative stability (corresponding to higher Tm) of nucleic acid hybridizations decreases in the following order: RNA:RNA, DNA:RNA, DNA:DNA. For hybrids of greater than 100 nucleotides in length, equations for calculating Tm have been derived (see Sambrook et al., supra, 9.50-9.51). For hybridizations with shorter nucleic acids, i.e., oligonucleotides, the position of mismatches becomes more important, and the length of the oligonucleotide determines its specificity (see Sambrook et al., supra, 11.7-11.8). In one embodiment the length for a hybridizable nucleic acid is at least about 10 nucleotides. Preferably a minimum length for a hybridizable nucleic acid is at least about 15 nucleotides; more preferably at least about 20 nucleotides; and most preferably the length is at least about 30 nucleotides. Furthermore, the skilled artisan will recognize that the temperature and wash solution salt concentration may be adjusted as necessary according to factors such as length of the probe.
A “substantial portion” of an amino acid or nucleotide sequence is that portion comprising enough of the amino acid sequence of a polypeptide or the nucleotide sequence of a gene to putatively identify that polypeptide or gene, either by manual evaluation of the sequence by one skilled in the art, or by computer-automated sequence comparison and identification using algorithms such as BLAST (Altschul, S. F., et al., J. Mol. Biol., 215:403-410 (1993)). In general, a sequence of ten or more contiguous amino acids or thirty or more nucleotides is necessary in order to putatively identify a polypeptide or nucleic acid sequence as homologous to a known protein or gene. Moreover, with respect to nucleotide sequences, gene specific oligonucleotide probes comprising 20-30 contiguous nucleotides may be used in sequence-dependent methods of gene identification (e.g., Southern hybridization) and isolation (e.g., in situ hybridization of bacterial colonies or bacteriophage plaques). In addition, short oligonucleotides of 12-15 bases may be used as amplification primers in PCR in order to obtain a particular nucleic acid fragment comprising the primers. Accordingly, a “substantial portion” of a nucleotide sequence comprises enough of the sequence to specifically identify and/or isolate a nucleic acid fragment comprising the sequence. The instant specification teaches the complete amino acid and nucleotide sequence encoding particular fungal proteins. The skilled artisan, having the benefit of the sequences as reported herein, may now use all or a substantial portion of the disclosed sequences for purposes known to those skilled in this art. Accordingly, the instant invention comprises the complete sequences as reported in the accompanying Sequence Listing, as well as substantial portions of those sequences as defined above.
The term “complementary” is used to describe the relationship between nucleotide bases that are capable of hybridizing to one another. For example, with respect to DNA, adenosine is complementary to thymine and cytosine is complementary to guanine.
The terms “homology” and “homologous” are used interchangeably herein. They refer to nucleic acid fragments wherein changes in one or more nucleotide bases do not affect the ability of the nucleic acid fragment to mediate gene expression or produce a certain phenotype. These terms also refer to modifications of the nucleic acid fragments of the instant invention such as deletion or insertion of one or more nucleotides that do not substantially alter the functional properties of the resulting nucleic acid fragment relative to the initial, unmodified fragment. It is therefore understood, as those skilled in the art will appreciate, that the invention encompasses more than the specific exemplary sequences.
Moreover, the skilled artisan recognizes that homologous nucleic acid sequences encompassed by this invention are also defined by their ability to hybridize, under moderately stringent conditions (e.g., 0.5×SSC, 0.1% SDS, 60° C.) with the sequences exemplified herein, or to any portion of the nucleotide sequences disclosed herein and which are functionally equivalent to any of the nucleic acid sequences disclosed herein.
“Codon degeneracy” refers to the nature in the genetic code permitting variation of the nucleotide sequence without effecting the amino acid sequence of an encoded polypeptide. The skilled artisan is well aware of the “codon-bias” exhibited by a specific host cell in usage of nucleotide codons to specify a given amino acid. Therefore, when synthesizing a gene for improved expression in a host cell, it is desirable to design the gene such that its frequency of codon usage approaches the frequency of preferred codon usage of the host cell.
The term “percent identity”, as known in the art, is a relationship between two or more polypeptide sequences or two or more polynucleotide sequences, as determined by comparing the sequences. In the art, “identity” also means the degree of sequence relatedness between polypeptide or polynucleotide sequences, as the case may be, as determined by the match between strings of such sequences. “Identity” and “similarity” can be readily calculated by known methods, including but not limited to those described in: 1.) Computational Molecular Biology (Lesk, A. M., Ed.) Oxford University: NY (1988); 2.) Biocomputing: Informatics and Genome Projects (Smith, D. W., Ed.) Academic: NY (1993); 3.) Computer Analysis of Sequence Data, Part I (Griffin, A. M., and Griffin, H. G., Eds.) Humania: NJ (1994); 4.) Sequence Analysis in Molecular Biology (von Heinje, G., Ed.) Academic (1987); and 5.) Sequence Analysis Primer (Gribskov, M. and Devereux, J., Eds.) Stockton: NY (1991).
Preferred methods to determine identity are designed to give the best match between the sequences tested. Methods to determine identity and similarity are codified in publicly available computer programs. Sequence alignments and percent identity calculations may be performed using the MegAlign™ program of the LASERGENE bioinformatics computing suite (DNASTAR Inc., Madison, Wis.). Multiple alignment of the sequences is performed using the “Clustal method of alignment” which encompasses several varieties of the algorithm including the “Clustal V method of alignment” corresponding to the alignment method labeled Clustal V (described by Higgins and Sharp, CABIOS. 5:151-153 (1989); Higgins, D. G. et al., Comput. Appl. Biosci., 8:189-191 (1992)) and found in the MegAlign™ program of the LASERGENE bioinformatics computing suite (DNASTAR Inc.). For multiple alignments, the default values correspond to GAP PENALTY=10 and GAP LENGTH PENALTY=10. Default parameters for pairwise alignments and calculation of percent identity of protein sequences using the Clustal method are KTUPLE=1, GAP PENALTY=3, WINDOW=5 and DIAGONALS SAVED=5. For nucleic acids these parameters are KTUPLE=2, GAP PENALTY=5, WINDOW=4 and DIAGONALS SAVED=4. After alignment of the sequences using the Clustal V program, it is possible to obtain a “percent identity” by viewing the “sequence distances” table in the same program. Additionally the “Clustal W method of alignment” is available and corresponds to the alignment method labeled Clustal W (described by Higgins and Sharp, CABIOS. 5:151-153 (1989); Higgins, D. G. et al., Comput. Appl. Biosci. 8:189-191 (1992)) and found in the MegAlign™ v6.1 program of the LASERGENE bioinformatics computing suite (DNASTAR Inc.). Default parameters for multiple alignment (GAP PENALTY=10, GAP LENGTH PENALTY=0.2, Delay Divergen Seqs(%)=30, DNA Transition Weight=0.5, Protein Weight Matrix=Gonnet Series, DNA Weight Matrix=IUB). After alignment of the sequences using the Clustal W program, it is possible to obtain a “percent identity” by viewing the “sequence distances” table in the same program.
It is well understood by one skilled in the art that many levels of sequence identity are useful in identifying polypeptides, from other species, wherein such polypeptides have the same or similar function or activity. Useful examples of percent identities include, but are not limited to: 24%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, or any integer percentage from 24% to 100% may be useful in describing the present invention, such as 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%. Suitable nucleic acid fragments not only have the above homologies but typically encode a polypeptide having at least 50 amino acids, preferably at least 100 amino acids, more preferably at least 150 amino acids, still more preferably at least 200 amino acids, and most preferably at least 250 amino acids.
The term “sequence analysis software” refers to any computer algorithm or software program that is useful for the analysis of nucleotide or amino acid sequences. “Sequence analysis software” may be commercially available or independently developed. Typical sequence analysis software will include, but is not limited to: 1.) the GCG suite of programs (Wisconsin Package Version 9.0, Genetics Computer Group (GCG), Madison, Wis.); 2.) BLASTP, BLASTN, BLASTX (Altschul et al., J. Mol. Biol., 215:403-410 (1990)); 3.) DNASTAR (DNASTAR, Inc. Madison, Wis.); 4.) Sequencher (Gene Codes Corporation, Ann Arbor, Mich.); and 5.) the FASTA program incorporating the Smith-Waterman algorithm (W. R. Pearson, Comput. Methods Genome Res., [Proc. Int. Symp.] (1994), Meeting Date 1992, 111-20. Editor(s): Suhai, Sandor. Plenum: New York, N.Y.). Within the context of this application it will be understood that where sequence analysis software is used for analysis, that the results of the analysis will be based on the “default values” of the program referenced, unless otherwise specified. As used herein “default values” will mean any set of values or parameters that originally load with the software when first initialized.
As used herein the term “coding sequence” refers to a DNA sequence that codes for a specific amino acid sequence. “Suitable regulatory sequences” refer to nucleotide sequences located upstream (5′ non-coding sequences), within, or downstream (3′ non-coding sequences) of a coding sequence, and which influence the transcription, RNA processing or stability, or translation of the associated coding sequence. Regulatory sequences may include promoters, translation leader sequences, introns, polyadenylation recognition sequences, RNA processing site, effector binding site and stem-loop structure.
The term “promoter” refers to a DNA sequence capable of controlling the expression of a coding sequence or functional RNA. In general, a coding sequence is located 3′ to a promoter sequence. Promoters may be derived in their entirety from a native gene, or be composed of different elements derived from different promoters found in nature, or even comprise synthetic DNA segments. It is understood by those skilled in the art that different promoters may direct the expression of a gene in different tissues or cell types, or at different stages of development, or in response to different environmental or physiological conditions. Promoters which cause a gene to be expressed in most cell types at most times are commonly referred to as “constitutive promoters”. It is further recognized that since in most cases the exact boundaries of regulatory sequences have not been completely defined, DNA fragments of different lengths may have identical promoter activity.
The term “operably linked” refers to the association of nucleic acid sequences on a single nucleic acid fragment so that the function of one is affected by the other. For example, a promoter is operably linked with a coding sequence when it is capable of effecting the expression of that coding sequence (i.e., that the coding sequence is under the transcriptional control of the promoter). Coding sequences can be operably linked to regulatory sequences in sense or antisense orientation.
The term “expression”, as used herein, refers to the transcription and stable accumulation of sense (mRNA) or antisense RNA derived from the nucleic acid fragment disclosed herein. Expression may also refer to translation of mRNA into a polypeptide.
As used herein the term “transformation” refers to the transfer of a nucleic acid fragment into a host organism, resulting in genetically stable inheritance. Host organisms containing the transformed nucleic acid fragments are referred to as “transgenic” or “recombinant” or “transformed” organisms.
The terms “plasmid” and “vector” refer to an extra chromosomal element often carrying genes which are not part of the central metabolism of the cell, and usually in the form of circular double-stranded DNA molecules. Such elements may be autonomously replicating sequences, genome integrating sequences, phage or nucleotide sequences, linear or circular, of a single- or double-stranded DNA or RNA, derived from any source, in which a number of nucleotide sequences have been joined or recombined into a unique construction which is capable of introducing a promoter fragment and DNA sequence for a selected gene product along with appropriate 3′ untranslated sequence into a cell. “Transformation vector” refers to a specific vector containing a foreign gene and having elements in addition to the foreign gene that facilitates transformation of a particular host cell.
As used herein the term “codon degeneracy” refers to the nature in the genetic code permitting variation of the nucleotide sequence without effecting the amino acid sequence of an encoded polypeptide. The skilled artisan is well aware of the “codon-bias” exhibited by a specific host cell in usage of nucleotide codons to specify a given amino acid. Therefore, when synthesizing a gene for improved expression in a host cell, it is desirable to design the gene such that its frequency of codon usage approaches the frequency of preferred codon usage of the host cell.
The term “codon-optimized” as it refers to genes or coding regions of nucleic acid molecules for transformation of various hosts, refers to the alteration of codons in the gene or coding regions of the nucleic acid molecules to reflect the typical codon usage of the host organism without altering the polypeptide encoded by the DNA.
Standard recombinant DNA and molecular cloning techniques used herein are well known in the art and are described by Sambrook, J., Fritsch, E. F. and Maniatis, T., Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (1989) (hereinafter “Maniatis”); and by Silhavy, T. J., Bennan, M. L. and Enquist, L. W., Experiments with Gene Fusions, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (1984); and by Ausubel, F. M. et al., Current Protocols in Molecular Biology, published by Greene Publishing Assoc. and Wiley-Interscience (1987).
Carbohydrate utilizing microorganisms employ the Embden-Meyerhof-Parnas (EMP) pathway, the Entner-Doudoroff pathway and the pentose phosphate cycle as the central, metabolic routes to provide energy and cellular precursors for growth and maintenance. These pathways have in common the intermediate glyceraldehyde-3-phosphate and, ultimately, pyruvate is formed directly or in combination with the EMP pathway. Subsequently, pyruvate is transformed to acetyl-coenzyme A (acetyl-CoA) via a variety of means. Acetyl-CoA serves as a key intermediate, for example, in generating fatty acids, amino acids and secondary metabolites. The combined reactions of sugar conversion to pyruvate produce energy (e.g. adenosine-5′-triphosphate, ATP) and reducing equivalents (e.g. reduced nicotinamide adenine dinucleotide, NADH, and reduced nicotinamide adenine dinucleotide phosphate, NADPH). NADH and NADPH must be recycled to their oxidized forms (NAD+ and NADP+, respectively). In the presence of inorganic electron acceptors (e.g. O2, NO3− and SO42−), the reducing equivalents may be used to augment the energy pool; alternatively, a reduced carbon by-product may be formed. As described by Donaldson et al., supra, isobutanol can be produced from carbohydrate sources by recombinant microorganisms comprising one of four complete isobutanol biosynthetic pathways, as shown in
Three of the pathways comprise conversion of pyruvate to isobutanol via a series of enzymatic steps. The preferred isobutanol pathway (
This pathway combines enzymes known to be involved in well-characterized pathways for valine biosynthesis (pyruvate to α-ketoisovalerate) and valine catabolism α-ketoisovalerate to isobutanol). Since many valine biosynthetic enzymes also catalyze analogous reactions in the isoleucine biosynthetic pathway, substrate specificity is a major consideration in selecting the gene sources. For this reason, the primary genes of interest for the acetolactate synthase enzyme are those from Bacillus (alsS) and Klebsiella (budB). These particular acetolactate synthases are known to participate in butanediol fermentation in these organisms and show increased affinity for pyruvate over ketobutyrate (Gollop et al., J. Bacteriol. 172(6):3444-3449 (1990); Holtzclaw et al., J. Bacteriol. 121(3):917-922 (1975)). The second and third pathway steps are catalyzed by acetohydroxy acid reductoisomerase and dehydratase, respectively. These enzymes have been characterized from a number of sources, such as for example, E. coli (Chunduru et al., Biochemistry 28(2):486-493 (1989); Flint et al., J. Biol. Chem. 268(29):14732-14742 (1993)). The final two steps of the preferred isobutanol pathway are known to occur in yeast, which can use valine as a nitrogen source and, in the process, secrete isobutanol. α-Ketoisovalerate can be converted to isobutyraldehyde by a number of keto acid decarboxylase enzymes, such as for example pyruvate decarboxylase. To prevent misdirection of pyruvate away from isobutanol production, a decarboxylase with decreased affinity for pyruvate is desired. So far, there are two such enzymes known in the art (Smit et al., Appl. Environ. Microbiol. 71(11):303-311 (2005); de la Plaza et al., FEMS Microbiol. Lett. 238(2):367-374 (2004)). Both enzymes are from strains of Lactococcus lactis and have a 50-200-fold preference for ketoisovalerate over pyruvate. Finally, a number of aldehyde reductases have been identified in yeast, many with overlapping substrate specificity. Those known to prefer branched-chain substrates over acetaldehyde include, but are not limited to, alcohol dehydrogenase VI (ADH6) and Ypr1p (Larroy et al., Biochem. J. 361 (Pt 1):163-172 (2002); Ford et al., Yeast 19(12):1087-1096 (2002)), both of which use NADPH as electron donor. An NADPH-dependent reductase, YqhD, active with branched-chain substrates has also been recently identified in E. coli (Sulzenbacher et al., J. Mol. Biol. 342(2):489-502 (2004)).
a) Pyruvate to acetolactate, is catalyzed by acetolactate synthase. The skilled person will appreciate that polypeptides having acetolactate synthase activity isolated from a variety of sources will be useful in the present invention independent of sequence homology. Example of suitable acetolactate synthase enzymes are available from a number of sources, for example, Bacillus subtilis (GenBank Nos: CAB15618 (SEQ ID NO:178), Z99122 (SEQ ID NO:78), NCBI (National Center for Biotechnology Information) amino acid sequence, NCBI nucleotide sequence, respectively), Klebsiella pneumoniae (GenBank Nos: AAA25079 (SEQ ID NO:2), M73842 (SEQ ID NO:1)), and Lactococcus lactis (GenBank Nos: AAA25161 (SEQ ID NO:180), L16975 (SEQ ID NO:179)). Preferred acetolactate synthase enzymes are those that have at least 80%-85% identity to SEQ ID NO:2, SEQ ID NO:178, and SEQ ID: 180 where at least 85%-90% identity is more preferred and where at least 95% identity based on the Clustal W method of alignment using the default parameters of GAP PENALTY=10, GAP LENGTH PENALTY=0.1, and Gonnet 250 series of protein weight matrix, is most preferred.
b) Acetolactate to 2,3-dihydroxyisovalerate, is catalyzed by acetohydroxy acid isomeroreductase. The skilled person will appreciate that polypeptides having acetohydroxy acid isomeroreductase activity isolated from a variety of sources will be useful in the present invention independent of sequence homology. Example of suitable acetohydroxy acid isomeroreductase enzymes are available from a number of sources, for example, Escherichia coli (GenBank Nos: NP—418222 (SEQ ID NO:4), NC—000913 (SEQ ID NO:3)), Saccharomyces cerevisiae (GenBank Nos: NP—013459 (SEQ ID NO:181), NC—001144 (SEQ ID NO:80)), Methanococcus maripaludis (GenBank Nos: CAF30210 (SEQ ID NO:183), BX957220 (SEQ ID NO:182)), and Bacillus. subtilis (GenBank Nos: CAB14789 (SEQ ID NO:185), Z99118 (SEQ ID NO:184)). Preferred acetohydroxy acid isomeroreductase enzymes are those that have at least 80%-85% identity to SEQ ID NO:43, SEQ ID NO:181, SEQ ID NO:183, and SEQ ID NO:185, where at least 85%-90% identity is more preferred and where at least 95% identity based on the Clustal W method of alignment using the default parameters of GAP PENALTY=10, GAP LENGTH PENALTY=0.1, and Gonnet 250 series of protein weight matrix, is most preferred.
c) 2,3-dihydroxyisovalerate to α-ketoisovalerate, as catalyzed for example by acetohydroxy acid dehydratase. The skilled person will appreciate that polypeptides having acetohydroxy acid dehydratase activity isolated from a variety of sources will be useful in the present invention independent of sequence homology. Example of suitable acetohydroxy acid dehydratase enzymes are available from a number of sources, for example, E. coli (GenBank Nos: YP—026248 (SEQ ID NO:6), NC—000913 (SEQ ID NO:5)), S. cerevisiae (GenBank Nos: NP—012550 (SEQ ID NO:186), NC—001142 (SEQ ID NO:83)), M. maripaludis (GenBank Nos: CAF29874 (SEQ ID NO:188), BX957219 (SEQ ID NO:187)), and B. subtilis (GenBank Nos: CAB14105 (SEQ ID NO:190), Z99115 (SEQ ID NO:189)). Preferred acetohydroxy acid dehydratase enzymes are those that have at least 80%-85% identity to SEQ ID NO:6, SEQ ID NO:186, SEQ ID NO:188, and SEQ ID NO:190, where at least 85%-90% identity is more preferred and where at least 95% identity based on the Clustal W method of alignment using the default parameters of GAP PENALTY=10, GAP LENGTH PENALTY=0.1, and Gonnet 250 series of protein weight matrix, is most preferred.
d) α-ketoisovalerate to isobutyraldehyde, as catalyzed for example by a branched-chain keto acid decarboxylase. The skilled person will appreciate that polypeptides having branched-chain keto acid decarboxylase activity isolated from a variety of sources will be useful in the present invention independent of sequence homology. Example of suitable branched-chain keto acid decarboxylase enzymes are available from a number of sources, for example, Lactococcus lactis (GenBank Nos: AAS49166 (SEQ ID NO:193), AY548760 (SEQ ID NO:192); CAG34226 (SEQ ID NO:8), AJ746364 (SEQ ID NO:191), Salmonella typhimurium (GenBank Nos: NP—461346 (SEQ ID NO:195), NC—003197 (SEQ ID NO:194)), and Clostridium acetobutylicum (GenBank Nos: NP—149189 (SEQ ID NO:197), NC—001988 (SEQ ID NO:196)). Preferred branched-chain keto acid decarboxylase enzymes are those that have at least 80%-85% identity to SEQ ID NO:8, SEQ ID NO:193, SEQ ID NO:195, and SEQ ID NO:197, where at least 85%-90% identity is more preferred and where at least 95% identity based on the Clustal W method of alignment using the default parameters of GAP PENALTY=10, GAP LENGTH PENALTY=0.1, and Gonnet 250 series of protein weight matrix, is most preferred.
e) Isobutyraldehyde to isobutanol, as catalyzed for example by, a branched-chain alcohol dehydrogenase. The skilled person will appreciate that polypeptides having branched-chain alcohol dehydrogenase activity isolated from a variety of sources will be useful in the present invention independent of sequence homology. Example of suitable branched-chain alcohol dehydrogenase enzymes are available from a number of sources, for example, S. cerevisiae (GenBank Nos: NP—010656 (SEQ ID NO:199), NC—001136 (SEQ ID NO:198); NP—014051 (SEQ ID NO:201) NC—001145 (SEQ ID NO:200)), E. coli (GenBank Nos: NP—417-484 (SEQ ID NO:10), NC—000913 (SEQ ID NO:9)), and C. acetobutylicum (GenBank Nos: NP—349892 (SEQ ID NO:203), NC—003030 (SEQ ID NO:202); NP—349891 (SEQ ID NO:204), NC—003030 (SEQ ID NO:158)). Preferred branched-chain alcohol dehydrogenase enzymes are those that have at least 80%-85% identity to SEQ ID NO:10, SEQ ID NO:199, SEQ ID NO:201, SEQ ID NO:203, and SEQ ID NO:204 where at least 85%-90% identity is more preferred and where at least 95% identity based on the Clustal W method of alignment using the default parameters of GAP PENALTY=10, GAP LENGTH PENALTY=0.1, and Gonnet 250 series of protein weight matrix, is most preferred.
Additional pathways are discussed below and in commonly owned and copending U.S. Ser. No. 11/586,315, incorporated herein by reference.
Another pathway for converting pyruvate to isobutanol comprises the following substrate to product conversions (
The first three steps in this pathway (a,b,c) are the same as those described above. The α-ketoisovalerate is converted to isobutyryl-CoA by the action of a branched-chain keto acid dehydrogenase. While yeast can only use valine as a nitrogen source, many other organisms (both eukaryotes and prokaryotes) can use valine as the carbon source as well. These organisms have branched-chain keto acid dehydrogenase (Sokatch et al. J. Bacteriol. 148(2):647-652 (1981)), which generates isobutyryl-CoA. Isobutyryl-CoA may be converted to isobutyraldehyde by an acylating aldehyde dehydrogenase. Dehydrogenases active with the branched-chain substrate have been described, but not cloned, in Leuconostoc and Propionibacterium (Kazahaya et al., J. Gen. Appl. Microbiol. 18:43-55 (1972); Hosoi et al., J. Ferment. Technol. 57:418-427 (1979)). However, it is also possible that acylating aldehyde dehydrogenases known to function with straight-chain acyl-CoAs (i.e. butyryl-CoA), may also work with isobutyryl-CoA. The isobutyraldehyde is then converted to isobutanol by a branched-chain alcohol dehydrogenase, as described above for the first pathway.
Another pathway for converting pyruvate to isobutanol comprises the following substrate to product conversions (
The first three steps in this pathway (a,b,c) are the same as those described above. This pathway requires the addition of a valine dehydrogenase or a suitable transaminase. Valine (and or leucine) dehydrogenase catalyzes reductive amination and uses ammonia; Km values for ammonia are in the millimolar range (Priestly et al., Biochem J. 261 (3):853-861 (1989); Vancura et al., J. Gen. Microbiol. 134(12):3213-3219 (1988) Zink et al., Arch. Biochem. Biophys. 99:72-77 (1962); Sekimoto et al. J. Biochem (Japan) 116(1):176-182 (1994)). Transaminases typically use either glutamate or alanine as amino donors and have been characterized from a number of organisms (Lee-Peng et al., J. Bacteriol. 139(2):339-345 (1979); Berg et al., J. Bacteriol. 155(3):1009-1014 (1983)). An alanine-specific enzyme may be desirable, since the generation of pyruvate from this step could be coupled to the consumption of pyruvate later in the pathway when the amine group is removed (see below). The next step is decarboxylation of valine, a reaction that occurs in valanimycin biosynthesis in Streptomyces (Garg et al., Mol. Microbiol. 46(2):505-517 (2002)). The resulting isobutylamine may be converted to isobutyraldehyde in a pyridoxal 5′-phosphate-dependent reaction by, for example, an enzyme of the omega-aminotransferase family. Such an enzyme from Vibrio fluvialis has demonstrated activity with isobutylamine (Shin et al., Biotechnol. Bioeng. 65(2):206-211 (1999)). Another omega-aminotransferase from Alcaligenes denitrificans has been cloned and has some activity with butylamine (Yun et al., Appl. Environ. Microbiol. 70(4):2529-2534 (2004)). In this direction, these enzymes use pyruvate as the amino acceptor, yielding alanine. As mentioned above, adverse affects on the pyruvate pool may be offset by using a pyruvate-producing transaminase earlier in the pathway. The isobutyraldehyde is then converted to isobutanol by a branched-chain alcohol dehydrogenase, as described above for the first pathway.
The fourth isobutanol biosynthetic pathway comprises the substrate to product conversions shown as steps k,g,e in
Thus, in providing multiple recombinant pathways from pyruvate to isobutanol, there exist a number of choices to fulfill the individual conversion steps, and the person of skill in the art will be able to utilize publicly available sequences to construct the relevant pathways. A listing of a representative number of genes known in the art and useful in the construction of isobutanol biosynthetic pathways are listed below in Table 2.
Microbial hosts for isobutanol production may be selected from bacteria, cyanobacteria, filamentous fungi and yeasts. The microbial host used for isobutanol production is preferably tolerant to isobutanol so that the yield is not limited by isobutanol toxicity. Microbes that are metabolically active at high titer levels of isobutanol are not well known in the art. Although 1-butanol-tolerant mutants have been isolated from solventogenic Clostridia, little information is available concerning the butanol tolerance of other potentially useful bacterial strains. Most of the studies on the comparison of alcohol tolerance in bacteria suggest that 1-butanol is more toxic than ethanol (de Cavalho et al., Microsc. Res. Tech. 64:215-22 (2004) and Kabelitz et al., FEMS Microbiol. Lett. 220:223-227 (2003)). Tomas et al. (J. Bacteriol. 186:2006-2018 (2004)) report that the yield of 1-butanol during fermentation in Clostridium acetobutylicum may be limited by 1-butanol toxicity. The primary effect of 1-butanol on Clostridium acetobutylicum is disruption of membrane functions (Hermann et al., Appl. Environ. Microbiol. 50:1238-1243 (1985)).
The microbial hosts selected for the production of isobutanol are preferably tolerant to isobutanol and should be able to convert carbohydrates to isobutanol. The criteria for selection of suitable microbial hosts include the following: intrinsic tolerance to isobutanol, high rate of glucose utilization, availability of genetic tools for gene manipulation, and the ability to generate stable chromosomal alterations.
Suitable host strains with a tolerance for isobutanol may be identified by screening based on the intrinsic tolerance of the strain. The intrinsic tolerance of microbes to isobutanol may be measured by determining the concentration of isobutanol that is responsible for 50% inhibition of the growth rate (IC50) when grown in a minimal medium. The IC50 values may be determined using methods known in the art. For example, the microbes of interest may be grown in the presence of various amounts of isobutanol and the growth rate monitored by measuring the optical density at 600 nanometers. The doubling time may be calculated from the logarithmic part of the growth curve and used as a measure of the growth rate. The concentration of isobutanol that produces 50% inhibition of growth may be determined from a graph of the percent inhibition of growth versus the isobutanol concentration. Preferably, the host strain should have an IC50 for isobutanol of greater than about 0.5%.
The microbial host for isobutanol production should also utilize glucose at a high rate. Most microbes are capable of utilizing carbohydrates. However, certain environmental microbes cannot utilize carbohydrates to high efficiency, and therefore would not be suitable hosts.
The ability to genetically modify the host is essential for the production of any recombinant microorganism. The mode of gene transfer technology may be by electroporation, conjugation, transduction or natural transformation. A broad range of host conjugative plasmids and drug resistance markers are available. The cloning vectors are tailored to the host organisms based on the nature of antibiotic resistance markers that can function in that host.
The microbial host also has to be manipulated in order to inactivate competing pathways for carbon flow by deleting various genes. This requires the availability of either transposons to direct inactivation or chromosomal integration vectors. Additionally, the production host should be amenable to chemical mutagenesis so that mutations to improve intrinsic isobutanol tolerance may be obtained.
Based on the criteria described above, suitable microbial hosts for the production of isobutanol include, but are not limited to, members of the genera Clostridium, Zymomonas, Escherichia, Salmonella, Rhodococcus, Pseudomonas, Bacillus, Lactobacillus, Enterococcus, Alcaligenes, Klebsiella, Paenibacillus, Arthrobacter, Corynebacterium, Brevibacterium, Pichia, Candida, Hansenula and Saccharomyces. Preferred hosts include: Escherichia coli, Alcaligenes eutrophus, Bacillus licheniformis, Paenibacillus macerans, Rhodococcus erythropolis, Pseudomonas putida, Lactobacillus plantarum, Enterococcus faecium, Enterococcus gallinarium, Enterococcus faecalis, Bacillus subtilis and Saccharomyces cerevisiae.
Recombinant organisms containing the necessary genes that will encode the enzymatic pathway for the conversion of a fermentable carbon substrate to isobutanol may be constructed using techniques well known in the art. Genes encoding the enzymes of one of the isobutanol biosynthetic pathways of the invention, for example, acetolactate synthase, acetohydroxy acid isomeroreductase, acetohydroxy acid dehydratase, branched-chain α-keto acid decarboxylase, and branched-chain alcohol dehydrogenase, may be isolated from various sources, as described above.
Methods of obtaining desired genes from a bacterial genome are common and well known in the art of molecular biology. For example, if the sequence of the gene is known, suitable genomic libraries may be created by restriction endonuclease digestion and may be screened with probes complementary to the desired gene sequence. Once the sequence is isolated, the DNA may be amplified using standard primer-directed amplification methods such as polymerase chain reaction (U.S. Pat. No. 4,683,202) to obtain amounts of DNA suitable for transformation using appropriate vectors. Tools for codon optimization for expression in a heterologous host are readily available. Some tools for codon optimization are available based on the GC content of the host organism. The GC content of some exemplary microbial hosts is given Table 3.
B. licheniformis
B. subtilis
C. acetobutylicum
E. coli
P. putida
A. eutrophus
Paenibacillus macerans
Rhodococcus erythropolis
Brevibacillus
Paenibacillus polymyxa
Once the relevant pathway genes are identified and isolated they may be transformed into suitable expression hosts by means well known in the art. Vectors or cassettes useful for the transformation of a variety of host cells are common and commercially available from companies such as EPICENTRE® (Madison, Wis.), Invitrogen Corp. (Carlsbad, Calif.), Stratagene (La Jolla, Calif.), and New England Biolabs, Inc. (Beverly, Mass.). Typically the vector or cassette contains sequences directing transcription and translation of the relevant gene, a selectable marker, and sequences allowing autonomous replication or chromosomal integration. Suitable vectors comprise a region 5′ of the gene which harbors transcriptional initiation controls and a region 3′ of the DNA fragment which controls transcriptional termination. Both control regions may be derived from genes homologous to the transformed host cell, although it is to be understood that such control regions may also be derived from genes that are not native to the specific species chosen as a production host.
Initiation control regions or promoters, which are useful to drive expression of the relevant pathway coding regions in the desired host cell are numerous and familiar to those skilled in the art. Virtually any promoter capable of driving these genetic elements is suitable for the present invention including, but not limited to, CYC1, HIS3, GAL1, GAL10, ADH1, PGK, PHO5, GAPDH, ADC1, TRP1, URA3, LEU2, ENO, TPI, CUP1, FBA, GPD, and GPM (useful for expression in Saccharomyces); AOX1 (useful for expression in Pichia); and lac, ara, tet, trp, IPL, IPR, T7, tac, and trc (useful for expression in Escherichia coli, Alcaligenes, and Pseudomonas); the amy, apr, npr promoters and various phage promoters useful for expression in Bacillus subtilis, Bacillus licheniformis, and Paenibacillus macerans; nisA (useful for expression Gram-positive bacteria, Eichenbaum et al. Appl. Environ. Microbiol. 64(8):2763-2769 (1998)); and the synthetic P11 promoter (useful for expression in Lactobacillus plantarum, Rud et al., Microbiology 152:1011-1019 (2006)).
Termination control regions may also be derived from various genes native to the preferred hosts. Optionally, a termination site may be unnecessary, however, it is most preferred if included.
Certain vectors are capable of replicating in a broad range of host bacteria and can be transferred by conjugation. The complete and annotated sequence of pRK404 and three related vectors-pRK437, pRK442, and pRK442(H) are available. These derivatives have proven to be valuable tools for genetic manipulation in Gram-negative bacteria (Scott et al., Plasmid 50(1):74-79 (2003)). Several plasmid derivatives of broad-host-range Inc P4 plasmid RSF1010 are also available with promoters that can function in a range of Gram-negative bacteria. Plasmid pAYC36 and pAYC37, have active promoters along with multiple cloning sites to allow for the heterologous gene expression in Gram-negative bacteria.
Chromosomal gene replacement tools are also widely available. For example, a thermosensitive variant of the broad-host-range replicon pWV101 has been modified to construct a plasmid pVE6002 which can be used to effect gene replacement in a range of Gram-positive bacteria (Maguin et al., J. Bacteriol. 174(17):5633-5638 (1992)). Additionally, in vitro transposomes are available to create random mutations in a variety of genomes from commercial sources such as EPICENTRE®.
The expression of an isobutanol biosynthetic pathway in various preferred microbial hosts is described in more detail below.
Expression of an Isobutanol Biosynthetic Pathway in E. coli
Vectors or cassettes useful for the transformation of E. coli are common and commercially available from the companies listed above. For example, the genes of an isobutanol biosynthetic pathway may be isolated from various sources, cloned into a modified pUC19 vector and transformed into E. coli NM522, as described in Examples 10 and 11.
Expression of an Isobutanol Biosynthetic Pathway in Rhodococcus erythropolis
A series of E. coli-Rhodococcus shuttle vectors are available for expression in R. erythropolis, including, but not limited to, pRhBR17 and pDA71 (Kostichka et al., Appl. Microbiol. Biotechnol. 62:61-68 (2003)). Additionally, a series of promoters are available for heterologous gene expression in R. erythropolis (see for example Nakashima et al., Appl. Environ. Microbiol. 70:5557-5568 (2004), and Tao et al., Appl. Microbiol. Biotechnol. 2005, DOI 10.1007/s00253-005-0064). Targeted gene disruption of chromosomal genes in R. erythropolis may be created using the method described by Tao et al., supra, and Brans et al. (Appl. Environ. Microbiol. 66: 2029-2036 (2000)).
The heterologous genes required for the production of isobutanol, as described above, may be cloned initially in pDA71 or pRhBR71 and transformed into E. coli. The vectors may then be transformed into R. erythropolis by electroporation, as described by Kostichka et al., supra. The recombinants may be grown in synthetic medium containing glucose and the production of isobutanol can be followed using methods known in the art.
Expression of an Isobutanol Biosynthetic Pathway in B. Subtilis
Methods for gene expression and creation of mutations in B. subtilis are also well known in the art. For example, the genes of an isobutanol biosynthetic pathway may be isolated from various sources, cloned into a modified pUC19 vector and transformed into Bacillus subtilis BE1010, as described in Example 12. Additionally, the five genes of an isobutanol biosynthetic pathway can be split into two operons for expression, as described in Example 24. The three genes of the pathway (bubB, ilvD, and kivD) were integrated into the chromosome of Bacillus subtilis BE1010 (Payne and Jackson, J. Bacteriol. 173:2278-2282 (1991)). The remaining two genes (ilvC and bdhB) were cloned into an expression vector and transformed into the Bacillus strain carrying the integrated isobutanol genes
Expression of an Isobutanol Biosynthetic Pathway in B. licheniformis
Most of the plasmids and shuttle vectors that replicate in B. subtilis may be used to transform B. licheniformis by either protoplast transformation or electroporation. The genes required for the production of isobutanol may be cloned in plasmids pBE20 or pBE60 derivatives (Nagarajan et al., Gene 114:121-126 (1992)). Methods to transform B. licheniformis are known in the art (for example see Fleming et al. Appl. Environ. Microbiol., 61(11):3775-3780 (1995)). The plasmids constructed for expression in B. subtilis may be transformed into B. licheniformis to produce a recombinant microbial host that produces isobutanol.
Expression of an Isobutanol Biosynthetic Pathway in Paenibacillus macerans
Plasmids may be constructed as described above for expression in B. subtilis and used to transform Paenibacillus macerans by protoplast transformation to produce a recombinant microbial host that produces isobutanol.
Expression of the Isobutanol Biosynthetic Pathway in Alcaligenes (Ralstonia) eutrophus
Methods for gene expression and creation of mutations in Alcaligenes eutrophus are known in the art (see for example Taghavi et al., Appl. Environ. Microbiol., 60(10):3585-3591 (1994)). The genes for an isobutanol biosynthetic pathway may be cloned in any of the broad host range vectors described above, and electroporated to generate recombinants that produce isobutanol. The poly(hydroxybutyrate) pathway in Alcaligenes has been described in detail, a variety of genetic techniques to modify the Alcaligenes eutrophus genome is known, and those tools can be applied for engineering an isobutanol biosynthetic pathway.
Expression of an Isobutanol Biosynthetic Pathway in Pseudomonas putida
Methods for gene expression in Pseudomonas putida are known in the art (see for example Ben-Bassat et al., U.S. Pat. No. 6,586,229, which is incorporated herein by reference). The isobutanol pathway genes may be inserted into pPCU18 and this ligated DNA may be electroporated into electrocompetent Pseudomonas putida DOT-T1 C5aAR1 cells to generate recombinants that produce isobutanol.
Expression of an Isobutanol Biosynthetic Pathway in Saccharomyces cerevisiae
Methods for gene expression in Saccharomyces cerevisiae are known in the art (see for example Methods in Enzymology, Volume 194, Guide to Yeast Genetics and Molecular and Cell Biology (Part A, 2004, Christine Guthrie and Gerald R. Fink (Eds.), Elsevier Academic Press, San Diego, Calif.). Expression of genes in yeast typically requires a promoter, followed by the gene of interest, and a transcriptional terminator. A number of yeast promoters can be used in constructing expression cassettes for genes encoding an isobutanol biosynthetic pathway, including, but not limited to constitutive promoters FBA, GPD, ADH1, and GPM, and the inducible promoters GAL1, GAL10, and CUP1. Suitable transcriptional terminators include, but are not limited to FBAt, GPDt, GPMt, ERG10t, GAL1t, CYC1, and ADH1. For example, suitable promoters, transcriptional terminators, and the genes of an isobutanol biosynthetic pathway may be cloned into E. coli-yeast shuttle vectors as described in Example 21.
Expression of an Isobutanol Biosynthetic Pathway in Lactobacillus plantarum
The Lactobacillus genus belongs to the Lactobacillales family and many plasmids and vectors used in the transformation of Bacillus subtilis and Streptococcus may be used for lactobacillus. Non-limiting examples of suitable vectors include pAMβ1 and derivatives thereof (Renault et al., Gene 183:175-182 (1996); and O'Sullivan et al., Gene 137:227-231 (1993)); pMBB1 and pHW800, a derivative of pMBB1 (Wyckoff et al. Appl. Environ. Microbiol. 62:1481-1486 (1996)); pMG1, a conjugative plasmid (Tanimoto et al., J. Bacteriol. 184:5800-5804 (2002)); pNZ9520 (Kleerebezem et al., Appl. Environ. Microbiol. 63:4581-4584 (1997)); pAM401 (Fujimoto et al., Appl. Environ. Microbiol. 67:1262-1267 (2001)); and pAT392 (Arthur et al., Antimicrob. Agents Chemother. 38:1899-1903 (1994)). Several plasmids from Lactobacillus plantarum have also been reported (e.g., van Kranenburg R, Golic N, Bongers R, Leer R J, de Vos W M, Siezen R J, Kleerebezem M. Appl. Environ. Microbiol. 2005 March; 71(3): 1223-1230). For example, expression of an isobutanol biosynthetic pathway in Lactobacillus plantarum is described in Example 25.
Expression of an Isobutanol Biosynthetic Pathway in Enterococcus faecium, Enterococcus gallinarium, and Enterococcus faecalis
The Enterococcus genus belongs to the Lactobacillales family and many plasmids and vectors used in the transformation of Lactobacillus, Bacillus subtilis, and Streptococcus may be used for Enterococcus. Non-limiting examples of suitable vectors include pAMβ1 and derivatives thereof (Renault et al., Gene 183:175-182 (1996); and O'Sullivan et al., Gene 137:227-231 (1993)); pMBB1 and pHW800, a derivative of pMBB1 (Wyckoff et al. Appl. Environ. Microbiol. 62:1481-1486 (1996)); pMG1, a conjugative plasmid (Tanimoto et al., J. Bacteriol. 184:5800-5804 (2002)); pNZ9520 (Kleerebezem et al., Appl. Environ. Microbiol. 63:4581-4584 (1997)); pAM401 (Fujimoto et al., Appl. Environ. Microbiol. 67:1262-1267 (2001)); and pAT392 (Arthur et al., Antimicrob. Agents Chemother. 38:1899-1903 (1994)). Expression vectors for E. faecalis using the nisA gene from Lactococcus may also be used (Eichenbaum et al., Appl. Environ. Microbiol. 64:2763-2769 (1998). Additionally, vectors for gene replacement in the E. faecium chromosome may be used (Nallaapareddy et al., Appl. Environ. Microbiol. 72:334-345 (2006)). For example, expression of an isobutanol biosynthetic pathway in Enterococcus faecalis is described in Example 26.
Fermentation media in the present invention must contain suitable carbon substrates. Suitable substrates may include but are not limited to monosaccharides such as glucose and fructose, oligosaccharides such as lactose or sucrose, polysaccharides such as starch or cellulose or mixtures thereof and unpurified mixtures from renewable feedstocks such as cheese whey permeate, cornsteep liquor, sugar beet molasses, and barley malt. Additionally the carbon substrate may also be one-carbon substrates such as carbon dioxide, or methanol for which metabolic conversion into key biochemical intermediates has been demonstrated. In addition to one and two carbon substrates methylotrophic organisms are also known to utilize a number of other carbon containing compounds such as methylamine, glucosamine and a variety of amino acids for metabolic activity. For example, methylotrophic yeast are known to utilize the carbon from methylamine to form trehalose or glycerol (Bellion et al., Microb. Growth C1 Compd., [Int. Symp.], 7th (1993), 415-32. Editor(s): Murrell, J. Collin; Kelly, Don P. Publisher: Intercept, Andover, UK). Similarly, various species of Candida will metabolize alanine or oleic acid (Sulter et al., Arch. Microbiol. 153:485-489 (1990)). Hence it is contemplated that the source of carbon utilized in the present invention may encompass a wide variety of carbon containing substrates and will only be limited by the choice of organism.
Although it is contemplated that all of the above mentioned carbon substrates and mixtures thereof are suitable in the present invention, preferred carbon substrates are glucose, fructose, and sucrose. Sucrose may be derived from renewable sugar sources such as sugar cane, sugar beets, cassaya, sweet sorghum, and mixtures thereof. Glucose and dextrose may be derived from renewable grain sources through saccharification of starch based feedstocks including grains such as corn, wheat, rye, barley, oats, and mixtures thereof. In addition, fermentable sugars may be derived from renewable cellulosic or lignocellulosic biomass through processes of pretreatment and saccharification, as described, for example, in co-owned and co-pending U.S. Patent Application Publication No. 2007/0031918A1, which is herein incorporated by reference. Biomass refers to any cellulosic or lignocellulosic material and includes materials comprising cellulose, and optionally further comprising hemicellulose, lignin, starch, oligosaccharides and/or monosaccharides. Biomass may also comprise additional components, such as protein and/or lipid. Biomass may be derived from a single source, or biomass can comprise a mixture derived from more than one source; for example, biomass may comprise a mixture of corn cobs and corn stover, or a mixture of grass and leaves. Biomass includes, but is not limited to, bioenergy crops, agricultural residues, municipal solid waste, industrial solid waste, sludge from paper manufacture, yard waste, wood and forestry waste. Examples of biomass include, but are not limited to, corn grain, corn cobs, crop residues such as corn husks, corn stover, grasses, wheat, wheat straw, barley, barley straw, hay, rice straw, switchgrass, waste paper, sugar cane bagasse, sorghum, soy, components obtained from milling of grains, trees, branches, roots, leaves, wood chips, sawdust, shrubs and bushes, vegetables, fruits, flowers, animal manure, and mixtures thereof.
In addition to an appropriate carbon source, fermentation media must contain suitable minerals, salts, cofactors, buffers and other components, known to those skilled in the art, suitable for the growth of the cultures and promotion of the enzymatic pathway necessary for isobutanol production.
Culture Conditions with Temperature Lowering
In the present method, the recombinant microbial production host which produces isobutanol is seeded into a fermentation medium comprising a fermentable carbon substrate to create a fermentation culture. The production host is grown in the fermentation culture at a first temperature for a first period of time. The first temperature is typically from about 25° C. to about 40° C.
Suitable fermentation media in the present invention include common commercially prepared media such as Luria Bertani (LB) broth, Sabouraud Dextrose (SD) broth or Yeast Medium (YM) broth. Other defined or synthetic growth media may also be used, and the appropriate medium for growth of the particular microorganism will be known by one skilled in the art of microbiology or fermentation science. The use of agents known to modulate catabolite repression directly or indirectly, e.g., cyclic adenosine 2′:3′-monophosphate, may also be incorporated into the fermentation medium.
Suitable pH ranges for the fermentation are between pH 5.0 to pH 9.0, where pH 6.0 to pH 8.0 is preferred as the initial condition.
Fermentations may be performed under aerobic or anaerobic conditions, where anaerobic or microaerobic conditions are preferred.
The first period of time to grow the production host at the first temperature may be determined in a variety of ways. For example, during this period of growth a metabolic parameter of the fermentation culture may be monitored. The metabolic parameter that is monitored may be any parameter known in the art, including, but not limited to the optical density, pH, respiratory quotient, fermentable carbon substrate utilization, CO2 production, and isobutanol production. During this period of growth, additional fermentable carbon substrate may be added, the pH may be adjusted, oxygen may be added for aerobic cells, or other culture parameters may be adjusted to support the metabolic activity of the culture. Though nutrients and culture conditions are supportive of growth, after a period of time the metabolic activity of the fermentation culture decreases as determined by the monitored parameter described above. For example, a decrease in metabolic activity may be indicated by a decrease in one or more of the following parameters: rate of optical density change, rate of pH change, rate of change in respiratory quotient (if the host cells are aerobic), rate of fermentable carbon substrate utilization, rate of isobutanol production, rate of change in CO2 production, or rate of another metabolic parameter. The decrease in metabolic activity is related to the sensitivity of the host cells to the production of isobutanol and/or the presence of isobutanol in the culture. When decreased metabolic activity is detected, the temperature of the fermentation culture is lowered to reduce the sensitivity of the host cells to isobutanol and thereby allow further production of isobutanol. In one embodiment, the lowering of the temperature coincides with a change in the metabolic parameter that is monitored.
In one embodiment, the change in metabolic activity is a decrease in the rate of isobutanol production. Isobutanol production may be monitored by analyzing the amount of isobutanol present in the fermentation culture medium as a function of time using methods well known in the art, such as using high performance liquid chromatography (HPLC) or gas chromatography (GC), which are described in the Examples herein. GC is preferred due to the short assay time.
Alternatively, the lowering of the temperature of the fermentation culture may occur at a predetermined time. The first period of time may be predetermined by establishing a correlation between a metabolic parameter of the fermentation culture and time in a series of test fermentations runs. A correlation between a metabolic parameter, as described above, and time of culture growth may be established for any isobutanol producing host by one skilled in the art. The specific correlation may vary depending on conditions used including, but not limited to, carbon substrate, fermentation conditions, and the specific recombinant isobutanol producing microbial production host. The correlation is most suitably made between isobutanol production or specific glucose consumption rate and time of culture growth. Once the predetermined time has been established from the correlation, the temperature of the fermentation culture in subsequent fermentation runs is lowered at the predetermined time. For example, if it is determined by monitoring a metabolic parameter in the test fermentation runs that the rate of production of isobutanol decreases after 12 hours, the temperature in subsequent fermentations runs is lowered after 12 hours without the need to monitor isobutanol production in the subsequent runs.
After the first period of time, the temperature of the fermentation culture is lowered to a second temperature. Typically, the second temperature is about 3° C. to about 25° C. lower than the first temperature. Reduction in temperature to enhance tolerance of the host cells to isobutanol is balanced with maintaining the temperature at a level where the cells continue to be metabolically active for isobutanol production. For example, a fermentation culture that has been grown at about 35° C. may be reduced in temperature to about 28° C.; or a culture grown at about 30° C. may be reduced in temperature to about 25° C. The change in temperature may be done gradually over time or may be made as a step change. The production host is incubated at the second temperature for a second period of time, so that isobutanol production continues. The second period of time may be determined in the same manner as the first period of time described above, e.g., by monitoring a metabolic parameter or by using a predetermined time.
Additionally, the temperature lowering and incubation steps may be repeated one or more times to more finely balance metabolic activity for isobutanol production and isobutanol sensitivity. For example, a culture that has been grown at about 35° C. may be reduced in temperature to about 32° C., followed by an incubation period. During this period a metabolic parameter of the fermentation culture may be monitored as described above, or a predetermined time may be used. It is particularly suitable to monitor the production of isobutanol during this incubation period. When monitoring indicates a decrease in metabolic activity or at a predetermined time, the temperature may be reduced a second time. For example, the temperature may be reduced from about 32° C. to about 28° C. The temperature lowering and incubation steps may be repeated a third time where the temperature is reduced, for example, to about 20° C. The production host is incubated at the lowered temperature so that isobutanol production continues. The steps may be repeated further as necessary to obtain the desired isobutanol titer.
The present process employs a batch method of fermentation. A classical batch fermentation is a closed system where the composition of the medium is set at the beginning of the fermentation and not subject to artificial alterations during the fermentation. Thus, at the beginning of the fermentation the medium is inoculated with the desired organism or organisms, and fermentation is permitted to occur without adding anything to the system. Typically, however, a “batch” fermentation is batch with respect to the addition of carbon source and attempts are often made at controlling factors such as pH and oxygen concentration. In batch systems the metabolite and biomass compositions of the system change constantly up to the time the fermentation is stopped. Within batch cultures cells moderate through a static lag phase to a high growth log phase and finally to a stationary phase where growth rate is diminished or halted. If untreated, cells in the stationary phase will eventually die. Cells in log phase generally are responsible for the bulk of production of end product or intermediate.
A variation on the standard batch system is the Fed-Batch system. Fed-Batch fermentation processes are also suitable in the present invention and comprise a typical batch system with the exception that the substrate is added in increments as the fermentation progresses. Fed-Batch systems are useful when catabolite repression is apt to inhibit the metabolism of the cells and where it is desirable to have limited amounts of substrate in the media. Measurement of the actual substrate concentration in Fed-Batch systems is difficult and is therefore estimated on the basis of the changes of measurable factors such as pH, dissolved oxygen and the partial pressure of waste gases such as CO2. Batch and Fed-Batch fermentations are common and well known in the art and examples may be found in Thomas D. Brock in Biotechnology: A Textbook of Industrial Microbiology, Second Edition (1989) Sinauer Associates, Inc., Sunderland, Mass., or Deshpande, Mukund V., Appl. Biochem. Biotechnol., 36:227, (1992), herein incorporated by reference.
Although the present invention is performed in batch mode it is contemplated that the method would be adaptable to continuous fermentation methods. Continuous fermentation is an open system where a defined fermentation medium is added continuously to a bioreactor and an equal amount of conditioned media is removed simultaneously for processing. Continuous fermentation generally maintains the cultures at a constant high density where cells are primarily in log phase growth.
Continuous fermentation allows for the modulation of one factor or any number of factors that affect cell growth or end product concentration. For example, one method will maintain a limiting nutrient such as the carbon source or nitrogen level at a fixed rate and allow all other parameters to moderate. In other systems a number of factors affecting growth can be altered continuously while the cell concentration, measured by media turbidity, is kept constant. Continuous systems strive to maintain steady state growth conditions and thus the cell loss due to the medium being drawn off must be balanced against the cell growth rate in the fermentation. Methods of modulating nutrients and growth factors for continuous fermentation processes as well as techniques for maximizing the rate of product formation are well known in the art of industrial microbiology and a variety of methods are detailed by Brock, supra.
It is contemplated that the present invention may be practiced using either batch, fed-batch or continuous processes and that any known mode of fermentation would be suitable. Additionally, it is contemplated that cells may be immobilized on a substrate as whole cell catalysts and subjected to fermentation conditions for isobutanol production.
Methods for Isobutanol Isolation from the Fermentation Medium
The bioproduced isobutanol may be isolated from the fermentation medium using methods known in the art. For example, solids may be removed from the fermentation medium by centrifugation, filtration, decantation, or the like. Then, the isobutanol may be isolated from the fermentation medium, which has been treated to remove solids as described above, using methods such as distillation, liquid-liquid extraction, or membrane-based separation. Because isobutanol forms a low boiling point, azeotropic mixture with water, distillation can only be used to separate the mixture up to its azeotropic composition. Distillation may be used in combination with another separation method to obtain separation around the azeotrope. Methods that may be used in combination with distillation to isolate and purify isobutanol include, but are not limited to, decantation, liquid-liquid extraction, adsorption, and membrane-based techniques. Additionally, isobutanol may be isolated using azeotropic distillation using an entrainer (see for example Doherty and Malone, Conceptual Design of Distillation Systems, McGraw Hill, New York, 2001).
The isobutanol-water mixture forms a heterogeneous azeotrope so that distillation may be used in combination with decantation to isolate and purify the isobutanol. In this method, the isobutanol containing fermentation broth is distilled to near the azeotropic composition. Then, the azeotropic mixture is condensed, and the isobutanol is separated from the fermentation medium by decantation. The decanted aqueous phase may be returned to the first distillation column as reflux. The isobutanol-rich decanted organic phase may be further purified by distillation in a second distillation column.
The isobutanol may also be isolated from the fermentation medium using liquid-liquid extraction in combination with distillation. In this method, the isobutanol is extracted from the fermentation broth using liquid-liquid extraction with a suitable solvent. The isobutanol-containing organic phase is then distilled to separate the isobutanol from the solvent.
Distillation in combination with adsorption may also be used to isolate isobutanol from the fermentation medium. In this method, the fermentation broth containing the isobutanol is distilled to near the azeotropic composition and then the remaining water is removed by use of an adsorbent, such as molecular sieves (Aden et al. Lignocellulosic Biomass to Ethanol Process Design and Economics Utilizing Co-Current Dilute Acid Prehydrolysis and Enzymatic Hydrolysis for Corn Stover, Report NREL/TP-510-32438, National Renewable Energy Laboratory, June 2002).
Additionally, distillation in combination with pervaporation may be used to isolate and purify the isobutanol from the fermentation medium. In this method, the fermentation broth containing the isobutanol is distilled to near the azeotropic composition, and then the remaining water is removed by pervaporation through a hydrophilic membrane (Guo et al., J. Membr. Sci. 245, 199-210 (2004)).
The present invention is further defined in the following Examples. It should be understood that these Examples, while indicating preferred embodiments of the invention, are given by way of illustration only. From the above discussion and these Examples, one skilled in the art can ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various uses and conditions.
Standard recombinant DNA and molecular cloning techniques used in the Examples are well known in the art and are described by Sambrook, J., Fritsch, E. F. and Maniatis, T. Molecular Cloning: A Laboratory Manual; Cold Spring Harbor Laboratory Press: Cold Spring Harbor, N.Y. (1989) (Maniatis) and by T. J. Silhavy, M. L. Bennan, and L. W. Enquist, Experiments with Gene Fusions, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (1984) and by Ausubel, F. M. et al., Current Protocols in Molecular Biology, pub. by Greene Publishing Assoc. and Wiley-Interscience (1987).
Materials and methods suitable for the maintenance and growth of bacterial cultures are well known in the art. Techniques suitable for use in the following Examples may be found as set out in Manual of Methods for General Bacteriology (Phillipp Gerhardt, R. G. E. Murray, Ralph N. Costilow, Eugene W. Nester, Willis A. Wood, Noel R. Krieg and G. Briggs Phillips, eds), American Society for Microbiology, Washington, D.C. (1994)) or by Thomas D. Brock in Biotechnology: A Textbook of Industrial Microbiology, Second Edition, Sinauer Associates, Inc., Sunderland, Mass. (1989). All reagents, restriction enzymes and materials used for the growth and maintenance of bacterial cells were obtained from Aldrich Chemicals (Milwaukee, Wis.), BD Diagnostic Systems (Sparks, Md.), Life Technologies (Rockville, Md.), or Sigma Chemical Company (St. Louis, Mo.) unless otherwise specified.
Microbial strains were obtained from The American Type Culture Collection (ATCC), Manassas, Va., unless otherwise noted.
The oligonucleotide primers to use in the following Examples are given in Table 4. All the oligonucleotide primers are synthesized by Sigma-Genosys (Woodlands, Tex.).
The concentration of isobutanol in the culture media can be determined by a number of methods known in the art. For example, a specific high performance liquid chromatography (HPLC) method utilized a Shodex SH-1011 column with a Shodex SH-G guard column, both purchased from Waters Corporation (Milford, Mass.), with refractive index (RI) detection. Chromatographic separation was achieved using 0.01 M H2SO4 as the mobile phase with a flow rate of 0.5 mL/min and a column temperature of 50° C. Isobutanol had a retention time of 46.6 min under the conditions used. Alternatively, gas chromatography (GC) methods are available. For example, a specific GC method utilized an HP-INNOWax column (30 m×0.53 mm id, 1 μm film thickness, Agilent Technologies, Wilmington, Del.), with a flame ionization detector (FID). The carrier gas was helium at a flow rate of 4.5 mL/min, measured at 150° C. with constant head pressure; injector split was 1:25 at 200° C.; oven temperature was 45° C. for 1 min, 45 to 220° C. at 10° C./min, and 220° C. for 5 min; and FID detection was employed at 240° C. with 26 mL/min helium makeup gas. The retention time of isobutanol was 4.5 min.
The meaning of abbreviations is as follows: “s” means second(s), “min” means minute(s), “h” means hour(s), “psi” means pounds per square inch, “nm” means nanometers, “d” means day(s), “μL” means microliter(s), “mL” means milliliter(s), “L” means liter(s), “mm” means millimeter(s), “nm” means nanometers, “mM” means millimolar, “μM” means micromolar, “M” means molar, “mmol” means millimole(s), “μmol” means micromole(s)”, “g” means gram(s), “μg” means microgram(s) and “ng” means nanogram(s), “PCR” means polymerase chain reaction, “OD” means optical density, “OD600” means the optical density measured at a wavelength of 600 nm, “kDa” means kilodaltons, “g” means the gravitation constant, “bp” means base pair(s), “kbp” means kilobase pair(s), “% w/v” means weight/volume percent, % v/v” means volume/volume percent, “IPTG” means isopropyl-β-D-thiogalactopyranoiside, “RBS” means ribosome binding site, “nt” means not tested, “HPLC” means high performance liquid chromatography, and “GC” means gas chromatography. The term “molar selectivity” is the number of moles of product produced per mole of sugar substrate consumed and is reported as a percent.
Tolerance levels of bacterial strain Lactobacillus plantarum PN0512 (ATCC # PTA-7727) were determined at 25° C., 30° C. and 37° C. as follows. The strain was cultured in S30L medium (i.e., 10 mM ammonium sulfate, 5 mM potassium phosphate buffer, pH 7.0, 50 mM MOPS, pH 7.0, 2 mM MgCl2, 0.7 mM CaCl2, 50 μM MnCl2, 1 μM FeCl3, 1 μM ZnCl2, 1.72 μM CuCl2, 2.53 μM COCl2, 2.42 μM Na2MoO4, 2 μM thiamine hydrochloride, 10 mM glucose, and 0.2% yeast extract). An overnight culture in the absence of any test compound was started in 15 mL of the S30L medium in a 150 mL flask, with incubation at 37° C. in a shaking water bath. The next morning, the overnight culture was diluted into three 500 mL flasks containing 150 mL of fresh medium to an initial OD600 of about 0.08. Each flask was incubated in a shaking water bath, one each at 25° C., 30° C. and 37° C. Each large culture was allowed to acclimate at the test temperature for at least 0.5 h. After the acclimation period, each large culture was split into flasks in the absence (control) and in the presence of various amounts of 1-butanol, isobutanol or 2-butanol, as listed in Tables 5, 6, and 7, respectively. Growth was followed by measuring OD600 for six hours after addition of the compounds. The results are summarized in Tables 5, 6, and 7 below.
All three butanols showed a similar effect of temperature on growth inhibition of L. plantarum PN0512. The concentration that resulted in full growth inhibition was greater at 25° C. than at 37° C. In the case of 1-butanol, growth was observed at 37° C. in 2.3% 1-butanol, but not 2.4%. However, at 30° C. growth was observed in 2.7%, but not 2.9%, and at 25° C. growth was observed even in 3.1% 1-butanol. Thus, the concentration of 1-butanol that completely inhibited growth increased as growth temperature decreased. Likewise, in the case of isobutanol, growth was observed in 3.5% at 25° C. while growth was observed in 3.1% at 30° C. and 37° C., but not in 3.3% or 3.4%. Similarly, in the case of 2-butanol growth was observed at 37° C. in 4.3%, but not in 4.5%; at 30° C. in 4.7%, but not in 4.9%; and at 25° C. in 5.2%. Thus the tolerance of L. plantarum PN0512 to butanols increased with decreased growth temperature.
The effect of growth and exposure temperature on survival of Escherichia coli in the presence of 1-butanol was tested using stationary phase cultures in a rich medium and log phase cultures in a defined medium. For the stationary phase studies, E. coli strain MG1655 (ATCC # 700926) was grown overnight in LB medium (Teknova, Half Moon Bay, Calif.) with shaking at 250 rpm at 42° C., 29° C. or 28° C. Survival of 1-butanol shock was tested at exposure temperatures of 0° C., 28° C. or 42° C. The 1-butanol exposure at 28° C. or 42° C. was started immediately after removing the overnight cultures from the growth incubators. The 1-butanol exposure at 0° C. was done after allowing the overnight cultures to cool on ice for about 15 min. A series of solutions of 1-butanol at different concentrations in LB medium was made and 90 μL aliquots were put in microfuge tubes. To these were added 10 μL of the overnight cultures and the tubes were immediately placed in shaking incubators at 42° C. or 28° C. or left on ice for 30 min. To stop the effect of 1-butanol on the cultures, a 10−2 dilution was done by placing 2 μL of the treated culture into 198 μL of LB medium in wells of a microplate. Then, 5 μL of the undiluted treated cultures were spotted on LB agar plates. Subsequent 10-fold serial dilutions of 10−3, 10−4, 10−5 and 10−6 of the exposed cultures were done by serial pipetting of 20 μL, starting with the 10−2 dilution cultures, into 180 μL of LB medium in the microplate, using a multi-channel pipette. Prior to each transfer, the cultures were mixed by pipetting up and down six times. Each dilution (5 μL) was spotted onto an LB plate using a multi-channel pipette and allowed to soak into the plate. The plates were inverted and incubated overnight at 37° C. The number of colonies for each dilution was counted and the % growth inhibition was calculated by comparison with a control culture that had not been exposed to 1-butanol. Survival of 0% was recorded when no colonies in the spots of the undiluted or any of the serial dilutions were observed. The results are shown in Table 8.
A similar study was done with log-phase cultures of E. coli grown in a defined medium. E. coli strain MG1655 was allowed to grow overnight in MOPS 0.2% glucose medium (Teknova, Half Moon Bay, Calif.) at 42° C. or 28° C. The following day, the cultures were diluted into fresh medium and allowed to grow at the same temperature until in the log phase of growth. The OD600 was 0.74 for the 28° C. culture and was 0.72 for the 42° C. culture. Both of these log phase cultures were exposed to 1-butanol at 42° C., 28° C. and 0° C. as follows. A series of solutions of 1-butanol at different concentrations in MOPS 0.2% glucose medium was made and 90 μL aliquots were put in microfuge tubes. To these were added 10 μL of the log phase cultures and the tubes were immediately placed in shaking incubators at 42° C. or 28° C. or left on ice for 30 min. To stop the effect of 1-butanol on the cultures, a 10−2 dilution was done by placing 2 μL of the treated culture into 198 μL of LB medium in wells of a microplate. Then 5 μL of the undiluted treated cultures were spotted on LB agar plates. Subsequent 10-fold serial dilutions of 10−3, 10−4, 10−5 and 10−6 of the exposed cultures were done by serial pipetting of 20 μL, starting with the 10−2 dilution cultures, into 180 μL of LB medium in the microplate, using a multi-channel pipette. Prior to each transfer, the cultures were mixed by pipetting up and down six times. Each dilution (5 μL) was spotted onto an LB plate using a multi-channel pipette and allowed to soak into the plate. The plates were inverted and incubated overnight at 37° C. The number of colonies for each dilution was counted and the % growth inhibition was calculated by comparison with a control culture that had not been exposed to 1-butanol. Survival of 0% was recorded when no colonies in the spots of the undiluted or any of the serial dilutions were observed. The results are shown in Table 9.
For both the stationary phase and log-phase cultures of E. coli MG1655, the growth temperature had very little, if any, effect on the survival of a 1-butanol shock. However, the exposure temperature had a major effect on the survival of E. coli to 1-butanol shock. As can be seen from the data in Tables 8 and 9, the tolerance of E. coli MG1655 to 1-butanol increased with decreasing exposure temperature.
The effect of exposure temperature on survival of Escherichia coli in the presence of 2-butanone (also referred to herein as methyl ethyl ketone or MEK) was tested as follows. E. coli strain BW25113 (The Coli Genetic Stock Center (CGSC), Yale University; # 7636) was grown overnight in LB medium (Teknova, Half Moon Bay, Calif.) with shaking at 250 rpm at 37° C. Survival of MEK shock was tested at exposure temperatures of 28° C. or 37° C. A series of solutions of MEK at different concentrations in LB medium was made and 90 μL aliquots were put in microfuge tubes. To these were added 10 μL of the overnight culture and the tubes were immediately placed in shaking incubators at 37° C. or 28° C. for 30 min. To stop the effect of MEK on the cultures, a 10−2 dilution was done by placing 2 μL of the MEK treated culture into 198 μL of LB medium in wells of a microplate. Then 5 μL of the undiluted treated cultures were spotted on LB agar plates. Subsequent 10-fold serial dilutions of 10−3, 10−4, 10−5 and 10−6 of the exposed cultures were done by serial pipetting of 20 μL, starting with the 10−2 dilution cultures, into 180 μL of LB medium in the microplate, using a multi-channel pipette. Prior to each transfer, the cultures were mixed by pipetting up and down six times. Each dilution (5 μL) was spotted onto LB plates using a multi-channel pipette and allowed to soak into the plate. The plates were inverted and incubated overnight at 37° C. The number of colonies for each dilution was counted and the % growth inhibition was calculated by comparison with a control culture that had not been exposed to MEK. Survival of 0% was recorded when no colonies in the spots of the undiluted or any of the serial dilutions were observed. The results, given as the average of duplicate experiments, are shown in Table 10.
Reducing the exposure temperature from 37° C. to 28° C. dramatically improved survival of E. coli to MEK treatment. At 37° C. there was full survival at 4% w/v and no survival at 6% w/v, while at 28° C. there was full survival at 6% w/v. Thus, the tolerance of E. coli to MEK increased with decreasing exposure temperature.
This Example demonstrates that the toxic effects of 1-butanol and 2-butanol on various microbial cells was reduced at lower temperatures. This was demonstrated by incubating E. coli (strain MG1655; ATCC # 700926), and L. plantarum (strain PN0512; ATCC # PTA-7727) with either 1-butanol or 2-butanol at different temperatures and then determining the fraction of the cells that survived the treatment at the different temperatures.
Using overnight cultures or cells from plates, 30 mL cultures of the microorganisms to be tested were started in the following culture media:
The results of experiments in which E. coli cells were treated with 1-butanol at temperatures of 0, 30, and 37° C. are shown Table 11.
The concentration at which 1-butanol kills E. coli cells was affected by the treatment temperature. At 0° C., concentrations of 1-butanol as high as 4.5% v/v had no toxic effect on E. coli cells during a one hour treatment. At 30° C., E. coli cells were killed when treated with 3% v/v 1-butanol for one hour. At 37° C., E. coli cells were killed when treated with 2% v/v 1-butanol for one hour.
The results of experiments in which L. plantarum PN0512 cells were treated with 1-butanol at temperatures of 0, 23, and 37° C. for one hour are shown Table 12.
The concentration at which 1-butanol kills L. plantarum PN0512 cells was affected by the treatment temperature. At 0° C., concentrations of 1-butanol as high as 4.5% v/v had no toxic effect on L. plantarum PN0512 cells during a one hour treatment. At 23° C., L. plantarum PN0512 cells were killed when treated with 3.5% v/v 1-butanol for one hour. At 37° C., L. plantarum PN0512 cells were killed when treated with 2.5% v/v 1-butanol for one hour.
The purpose of this Example was to clone the budB gene from Klebsiella pneumoniae and express it in E. coli BL21-AI. The budB gene was amplified from Klebsiella pneumoniae strain ATCC 25955 genomic DNA using PCR, resulting in a 1.8 kbp product.
Genomic DNA was prepared using the Gentra Puregene kit (Gentra Systems, Inc., Minneapolis, Minn.; catalog number D-5000A). The budB gene was amplified from Klebsiella pneumoniae genomic DNA by PCR using primers N80 and N81 (see Table 2), given as SEQ ID NOs:11 and 12, respectively. Other PCR amplification reagents were supplied in manufacturers' kits, for example, Finnzymes Phusion™ High-Fidelity PCR Master Mix (New England Biolabs Inc., Beverly, Mass.; catalog no. F-531) and used according to the manufacturer's protocol. Amplification was carried out in a DNA Thermocycler GeneAmp 9700 (PE Applied Biosystems, Foster city, Calif.).
For expression studies the Gateway cloning technology (Invitrogen Corp., Carlsbad, Calif.) was used. The entry vector PENTRSDD-TOPO allowed directional cloning and provided a Shine-Dalgamo sequence for the gene of interest. The destination vector pDEST14 used a T7 promoter for expression of the gene with no tag. The forward primer incorporated four bases (CACC) immediately adjacent to the translational start codon to allow directional cloning into PENTRSDD-TOPO (Invitrogen) to generate the plasmid pENTRSDD-TOPObudB. The pENTR construct was transformed into E. coli Top10 (Invitrogen) cells and plated according to manufacturer's recommendations. Transformants were grown overnight and plasmid DNA was prepared using the QIAprep Spin Miniprep kit (Qiagen, Valencia, Calif.; catalog no. 27106) according to manufacturer's recommendations. Clones were sequenced to confirm that the genes inserted in the correct orientation and to confirm the sequence. The nucleotide sequence of the open reading frame (ORF) for this gene and the predicted amino acid sequence of the enzyme are given as SEQ ID NO:1 and SEQ ID NO:2, respectively.
To create an expression clone, the budB gene was transferred to the pDEST 14 vector by recombination to generate pDEST14budB. The pDEST14budB vector was transformed into E. coli BL21-AI cells (Invitrogen). Transformants were inoculated into Luria Bertani (LB) medium supplemented with 50 μg/mL of ampicillin and grown overnight. An aliquot of the overnight culture was used to inoculate 50 mL of LB supplemented with 50 μg/mL of ampicillin. The culture was incubated at 37° C. with shaking until the OD600 reached 0.6-0.8. The culture was split into two 25-mL cultures and arabinose was added to one of the flasks to a final concentration of 0.2% w/v. The negative control flask was not induced with arabinose. The flasks were incubated for 4 h at 37° C. with shaking. Cells were harvested by centrifugation and the cell pellets were resuspended in 50 mM MOPS, pH 7.0 buffer. The cells were disrupted either by sonication or by passage through a French Pressure Cell. The whole cell lysate was centrifuged yielding the supernatant or cell free extract and the pellet or the insoluble fraction. An aliquot of each fraction (whole cell lysate, cell free extract and insoluble fraction) was resuspended in SDS (MES) loading buffer (Invitrogen), heated to 85° C. for 10 min and subjected to SDS-PAGE analysis (NuPAGE 4-12% Bis-Tris Gel, catalog no. NP0322Box, Invitrogen). A protein of the expected molecular weight of about 60 kDa, as deduced from the nucleic acid sequence, was present in the induced culture but not in the uninduced control.
Acetolactate synthase activity in the cell free extracts is measured using the method described by Bauerle et al. (Biochim. Biophys. Acta 92(1):142-149 (1964)).
The purpose of this prophetic Example is to describe how to clone the ilvC gene from E. coli K12 and express it in E. coli BL21-AI. The ilvC gene is amplified from E. coli genomic DNA using PCR.
The ilvC gene is cloned and expressed in the same manner as the budB gene described in Example 5. Genomic DNA from E. coli is prepared using the Gentra Puregene kit (Gentra Systems, Inc., Minneapolis, Minn.; catalog number D-5000A). The ilvC gene is amplified by PCR using primers N100 and N101 (see Table 2), given as SEQ ID NOs:13 and 14, respectively, creating a 1.5 kbp product. The forward primer incorporates four bases (CCAC) immediately adjacent to the translational start codon to allow directional cloning into pENTR/SD/D-TOPO (Invitrogen) to generate the plasmid pENTRSDD-TOPOilvC. Clones are sequenced to confirm that the genes are inserted in the correct orientation and to confirm the sequence. The nucleotide sequence of the open reading frame (ORF) for this gene and the predicted amino acid sequence of the enzyme are given as SEQ ID NO:3 and SEQ ID NO:4, respectively.
To create an expression clone, the ilvC gene is transferred to the pDEST 14 (Invitrogen) vector by recombination to generate pDEST14ilvC. The pDEST14ilvC vector is transformed into E. coli BL21-AI cells and expression from the T7 promoter is induced by addition of arabinose. A protein of the expected molecular weight of about 54 kDa, as deduced from the nucleic acid sequence, is present in the induced culture, but not in the uninduced control.
Acetohydroxy acid reductoisomerase activity in the cell free extracts is measured using the method described by Arfin and Umbarger (J. Biol. Chem. 244(5):1118-1127 (1969)).
The purpose of this prophetic Example is to describe how to clone the ilvD gene from E. coli K12 and express it in E. coli BL21-AI. The ilvD gene is amplified from E. coli genomic DNA using PCR.
The ilvD gene is cloned and expressed in the same manner as the budB gene described in Example 5. Genomic DNA from E. coli is prepared using the Gentra Puregene kit (Gentra Systems, Inc., Minneapolis, Minn.; catalog number D-5000A). The ilvD gene is amplified by PCR using primers N102 and N103 (see Table 2), given as SEQ ID NOs:15 and 16, respectively, creating a 1.9 kbp product. The forward primer incorporates four bases (CCAC) immediately adjacent to the translational start codon to allow directional cloning into pENTR/SD/D-TOPO (Invitrogen) to generate the plasmid pENTRSDD-TOPOilvD. Clones are submitted for sequencing to confirm that the genes are inserted in the correct orientation and to confirm the sequence. The nucleotide sequence of the open reading frame (ORF) for this gene and the predicted amino acid sequence of the enzyme are given as SEQ ID NO:5 and SEQ ID NO:6, respectively.
To create an expression clone, the ilvD gene is transferred to the pDEST 14 (Invitrogen) vector by recombination to generate pDEST14ilvD. The pDEST14ilvD vector is transformed into E. coli BL21-AI cells and expression from the T7 promoter is induced by addition of arabinose. A protein of the expected molecular weight of about 66 kDa, as deduced from the nucleic acid sequence, is present in the induced culture, but not in the uninduced control.
Acetohydroxy acid dehydratase activity in the cell free extracts is measured using the method described by Flint et al. (J. Biol. Chem. 268(20):14732-14742 (1993)).
The purpose of this prophetic example is to describe how to clone the kivD gene from Lactococcus lactis and express it in E. coli BL21-AI.
A DNA sequence encoding the branched-chain keto acid decarboxylase (kivD) from L. lactis is obtained from GenScript (Piscataway, N.J.). The sequence obtained is codon-optimized for expression in both E. coli and B. subtilis and is cloned into pUC57, to form pUC57-kivD. The codon-optimized nucleotide sequence of the open reading frame (ORF) for this gene and the predicted amino acid sequence of the enzyme are given as SEQ ID NO:7 and SEQ ID NO:8, respectively.
To create an expression clone NdeI and BamHI restriction sites are utilized to clone the 1.7 kbp kivD fragment from pUC57-kivD into vector pET-3a (Novagen, Madison, Wis.). This creates the expression clone pET-3a-kivD. The pET-3a-kivD vector is transformed into E. coli BL21-AI cells and expression from the T7 promoter is induced by addition of arabinose. A protein of the expected molecular weight of about 61 kDa, as deduced from the nucleic acid sequence, is present in the induced culture, but not in the uninduced control.
Branched-chain keto acid decarboxylase activity in the cell free extracts is measured using the method described by Smit et al. (Appl. Microbiol. Biotechnol. 64:396-402 (2003)).
The purpose of this prophetic Example is to describe how to clone the yqhD gene from E. coli K12 and express it in E. coli BL21-AI. The yqhD gene is amplified from E. coli genomic DNA using PCR.
The yqhD gene is cloned and expressed in the same manner as the budB gene described in Example 5. Genomic DNA from E. coli is prepared using the Gentra Puregene kit (Gentra Systems, Inc., Minneapolis, Minn.; catalog number D-5000A). The yqhD gene is amplified by PCR using primers N104 and N105 (see Table 2), given as SEQ ID NOs:17 and 18, respectively, creating a 1.2 kbp product. The forward primer incorporates four bases (CCAC) immediately adjacent to the translational start codon to allow directional cloning into pENTR/SD/D-TOPO (Invitrogen) to generate the plasmid pENTRSDD-TOPOyqhD. Clones are submitted for sequencing to confirm that the genes are inserted in the correct orientation and to confirm the sequence. The nucleotide sequence of the open reading frame (ORF) for this gene and the predicted amino acid sequence of the enzyme are given as SEQ ID NO 9 and SEQ ID NO:10, respectively.
To create an expression clone, the yqhD gene is transferred to the pDEST 14 (Invitrogen) vector by recombination to generate pDEST14yqhD. The pDEST14ilvD vector is transformed into E. coli BL21-AI cells and expression from the T7 promoter is induced by addition of arabinose. A protein of the expected molecular weight of about 42 kDa, as deduced from the nucleic acid sequence, is present in the induced culture, but not in the uninduced control.
Branched-chain alcohol dehydrogenase activity in the cell free extracts is measured using the method described by Sulzenbacher et al. (J. Mol. Biol. 342(2):489-502 (2004)).
The purpose of this prophetic Example is to describe how to construct a transformation vector comprising the genes encoding the five steps in an isobutanol biosynthetic pathway. All genes are placed in a single operon under the control of a single promoter. The individual genes are amplified by PCR with primers that incorporate restriction sites for later cloning and the forward primers contain an optimized E. coli ribosome binding site (AAAGGAGG). PCR products are TOPO cloned into the pCR 4Blunt-TOPO vector and transformed into E. coli Top10 cells (Invitrogen). Plasmid DNA is prepared from the TOPO clones and the sequence of the genes is verified. Restriction enzymes and T4 DNA ligase (New England Biolabs, Beverly, Mass.) are used according to manufacturer's recommendations. For cloning experiments, restriction fragments are gel-purified using QIAquick Gel Extraction kit (Qiagen). After confirmation of the sequence, the genes are subcloned into a modified pUC19 vector as a cloning platform. The pUC19 vector is modified by HindIII/SapI digestion, creating pUC19dHS. The digest removes the lac promoter adjacent to the MCS (multiple cloning site), preventing transcription of the operons in the vector.
The budB gene is amplified from K. pneumoniae ATCC 25955 genomic DNA by PCR using primer pair N110 and N111 (see Table 2), given as SEQ ID NOs:19 and 20, respectively, creating a 1.8 kbp product. The forward primer incorporates SphI and AflII restriction sites and a ribosome binding site (RBS). The reverse primer incorporates PacI and NsiI restriction sites. The PCR product is cloned into pCR4Blunt-TOPO creating pCR4Blunt-TOPO-budB. Plasmid DNA is prepared from the TOPO clones and the sequence of the gene is verified.
The ilvC gene is amplified from E. coli K12 genomic DNA by PCR using primer pair N112 and N113 (see Table 2) given as SEQ ID NOs:21 and 22, respectively, creating a 1.5 kbp product. The forward primer incorporates SalI and NheI restriction sites and a RBS. The reverse primer incorporates a XbaI restriction site. The PCR product is cloned into pCR4 Blunt-TOPO creating pCR4Blunt-TOPO-ilvC. Plasmid DNA is prepared from the TOPO clones and the sequence of the gene is verified.
The ilvD gene is amplified from E. coli K12 genomic DNA by PCR using primer pair N114 and N115 (see Table 2) given as SEQ ID NOs:23 and 24, respectively, creating a 1.9 kbp product. The forward primer incorporates a XbaI restriction site and a RBS. The reverse primer incorporates a BamHI restriction site. The PCR product is cloned into pCR4Blunt-TOPO creating pCR4Blunt-TOPO-ilvD. Plasmid DNA is prepared from the TOPO clones and the sequence of the gene is verified.
The kivD gene is amplified from pUC57-kivD (described in Example 8) by PCR using primer pair N116 and N117 (see Table 2), given as SEQ ID NOs:25 and 26, respectively, creating a 1.7 bp product. The forward primer incorporates a BamHI restriction site and a RBS. The reverse primer incorporates a SacI restriction site. The PCR product is cloned into pCR4Blunt-TOPO creating pCR4Blunt-TOPO-kivD. Plasmid DNA is prepared from the TOPO clones and the sequence of the gene is verified.
The yqhD gene is amplified from E. coli K12 genomic DNA by PCR using primer pair N118 and N119 (see Table 2) given as SEQ ID NOs:27 and 28, respectively, creating a 1.2 kbp product. The forward primer incorporates a SacI restriction site. The reverse primer incorporates SpeI and EcoRI restriction sites. The PCR product is cloned into pCR4Blunt-TOPO creating pCR4Blunt-TOPO-yqhD. Plasmid DNA is prepared from the TOPO clones and the sequence of the gene is verified.
To construct the isobutanol pathway operon, the yqhD gene is excised from pCR4Blunt-TOPO-yqhD with SacI and EcoRI, releasing a 1.2 kbp fragment. This is ligated with pUC19dHS, which has previously been digested with SacI and EcoRI. The resulting clone, pUC19dHS-yqhD, is confirmed by restriction digest. Next, the ilvC gene is excised from pCR4Blunt-TOPO-ilvC with SalI and XbaI, releasing a 1.5 kbp fragment. This is ligated with pUC19dHS-yqhD, which has previously been digested with SalI and XbaI. The resulting clone, pUC19dHS-ilvC-yqhD, is confirmed by restriction digest. The budB gene is then excised from pCR4Blunt-TOPO-budB with SphI and NsiI, releasing a 1.8 kbp fragment. pUC19dHS-ilvC-yqhD is digested with SphI and PstI and ligated with the SphI/NsiI budB fragment (NsiI and PstI generate compatible ends), forming pUC19dHS-budB-ilvC-yqhD. A 1.9 kbp fragment containing the ilvD gene is excised from pCR4Blunt-TOPO-ilvD with XbaI and BamHI and ligated with pUC19dHS-budB-ilvC-yqhD, which is digested with these same enzymes, forming pUC19dHS-budB-ilvC-ilvD-yqhD. Finally, kivD is excised from pCR4Blunt-TOPO-kivD with BamHI and SacI, releasing a 1.7 kbp fragment. This fragment is ligated with pUC19dHS-budB-ilvC-ilvD-yqhD, which has previously been digested with BamHI and SacI, forming pUC19dHS-budB-ilvC-ilvD-kivD-yqhD.
The pUC19dHS-budB-ilvC-ilvD-kivD-yqhD vector is digested with AflII and SpeI to release a 8.2 kbp operon fragment that is cloned into pBenAS, an E. coli-B. subtilis shuttle vector. Plasmid pBenAS is created by modification of the pBE93 vector, which is described by Nagarajan, (WO 93/24631, Example 4). To make pBenAS the Bacillus amyloliquefaciens neutral protease promoter (NPR), signal sequence, and the phoA gene are removed with a NcoI/HindIII digest of pBE93. The NPR promoter is PCR amplified from pBE93 by primers BenNF and BenASR, given as SEQ ID NOS:29 and 30, respectively. Primer BenASR incorporates AflII, SpeI, and HindIII sites downstream of the promoter. The PCR product is digested with NcoI and HindIII and the fragment is cloned into the corresponding sites in the vector creating pBenAS. The operon fragment is subcloned into the AflII and SpeI sites in pBenAS creating pBen-budB-ilvC-ilvD-kivD-yqhD.
The purpose of this prophetic Example is to describe how to express an isobutanol biosynthetic pathway in E. coli.
The plasmid pBen-budB-ilvC-ilvD-kivD-yqhD, constructed as described in Example 10, is transformed into E. coli NM522 (ATCC No. 47000) to give E. coli strain NM522/pBen-budB-ilvC-ilvD-kivD-yqhD and expression of the genes in the operon is monitored by SDS-PAGE analysis, enzyme assay and Western blot analysis. For Western blots, antibodies are raised to synthetic peptides by Sigma-Genosys (The Woodlands, Tex.).
E. coli strain NM522/pBen-budB-ilvC-ilvD-kivD-yqhD is inoculated into a 250 mL shake flask containing 50 mL of medium and shaken at 250 rpm and 35° C. The medium is composed of: glucose (5 g/L), MOPS (0.05 M), ammonium sulfate (0.01 M), potassium phosphate, monobasic (0.005 M), S10 metal mix (1% (v/v)) yeast extract (0.1% (w/v)), casamino acids (0.1% (w/v)), thiamine (0.1 mg/L), proline (0.05 mg/L), and biotin (0.002 mg/L), and is titrated to pH 7.0 with KOH. S10 metal mix contains: MgCl2 (200 mM), CaCl2 (70 mM), MnCl2 (5 mM), FeCl3 (0.1 mM), ZnCl2 (0.1 mM), thiamine hydrochloride (0.2 mM), CuSO4 (172 μM), COCl2 (253 μM), and Na2MoO4 (242 μM). After 18 h, isobutanol is detected by HPLC or GC analysis, using methods that are well known in the art, for example, as described in the General Methods section above.
The purpose of this prophetic Example is to describe how to express an isobutanol biosynthetic pathway in Bacillus subtilis. The same approach as described in Example 11 is used.
The plasmid pBen-budB-ilvC-ilvD-kivD-yqhD, constructed as described in Example 10, is used. This plasmid is transformed into Bacillus subtilis BE1010 (J. Bacteriol. 173:2278-2282 (1991)) to give B. subtilis strain BE1010/pBen-budB-ilvC-ilvD-kivD-yqhD and expression of the genes in each operon is monitored as described in Example 11.
B. subtilis strain BE1010/pBen-budB-ilvC-ilvD-kivD-yqhD is inoculated into a 250 mL shake flask containing 50 mL of medium and shaken at 250 rpm and 35° C. for 18 h. The medium is composed of: dextrose (5 g/L), MOPS (0.05 M), glutamic acid (0.02 M), ammonium sulfate (0.01 M), potassium phosphate, monobasic buffer (0.005 M), S10 metal mix (as described in Example 11, 1% (v/v)), yeast extract (0.1% (w/v)), casamino acids (0.1% (w/v)), tryptophan (50 mg/L), methionine (50 mg/L), and lysine (50 mg/L), and is titrated to pH 7.0 with KOH. After 18 h, isobutanol is detected by HPLC or GC analysis using methods that are well known in the art, for example, as described in the General Methods section above.
To create another acetolactate synthase expression clone, the budB gene was cloned into the vector pTrc99A. The budB gene was first amplified from pENTRSDD-TOPObudB (described in Example 5) using primers (N110.2 and N111.2, given as SEQ ID NOs:31 and 32, respectively) that introduced SacI, SpeI and MfeI sites at the 5′ end and BbvCI, AflII, and BamHI sites at the 3′ end. The resulting 1.75 kbp PCR product was cloned into pCR4-Blunt TOPO (Invitrogen) and the DNA sequence was confirmed (using N130Seq sequencing primers F1-F4 and R1-R4, given as SEQ ID NOs:40-47, respectively). The budB gene was then excised from this vector using SacI and BamHI and cloned into pTrc99A (Amann et al. Gene 69(2):301-315 (1988)), generating pTrc99A::budB. The pTrc99A::budB vector was transformed into E. coli TOP10 cells and the transformants were inoculated into LB medium supplemented with 50 μg/mL of ampicillin and grown overnight at 37° C. An aliquot of the overnight culture was used to inoculate 50 mL of LB medium supplemented with 50 μg/mL of ampicillin. The culture was incubated at 37° C. with shaking until the OD600 reached 0.6 to 0.8. Expression of budB from the Trc promoter was then induced by the addition of 0.4 mM IPTG. Negative control flasks were also prepared that were not induced with IPTG. The flasks were incubated for 4 h at 37° C. with shaking. Cell-free extracts were prepared as described in Example 5.
Acetolactate synthase activity in the cell free extracts was measured as described in Example 5. Three hours after induction with IPTG, an acetolactate synthase activity of 8 units/mg was detected. The control strain carrying only the pTrc99A plasmid exhibited 0.03 units/mg of acetolactate synthase activity.
The purpose of this Example was to clone the ilvC gene from E. coli K12 and express it in E. coli TOP10. The ilvC gene was amplified from E. coli K12 strain FM5 (ATCC 53911) genomic DNA using PCR.
The ilvC gene was cloned and expressed in a similar manner as described for the cloning and expression of ilvC in Example 6 above. PCR was used to amplify ilvC from the E. coli FM5 genome using primers N112.2 and N113.2 (SEQ ID NOs:33 and 34, respectively). The primers created SacI and AfllII sites and an optimal RBS at the 5′ end and NotI, NheI and BamHI sites at the 3′ end of ilvC. The 1.5 kbp PCR product was cloned into pCR4Blunt TOPO according to the manufacturer's protocol (Invitrogen) generating pCR4Blunt TOPO::ilvC. The sequence of the PCR product was confirmed using sequencing primers (N131SeqF1-F3, and N131SeqR1-R3, given as SEQ ID NOs:48-53, respectively). To create an expression clone, the ilvC gene was excised from pCR4Blunt TOPO::ilvC using SacI and BamHI and cloned into pTrc99A. The pTrc99A::ilvC vector was transformed into E. coli TOP10 cells and expression from the Trc promoter was induced by addition of IPTG, as described in Example 13. Cell-free extracts were prepared as described in Example 5.
Acetohydroxy acid reductoisomerase activity in the cell free extracts was measured as described in Example 6. Three hours after induction with IPTG, an acetohydroxy acid reductoisomerase activity of 0.026 units/mg was detected. The control strain carrying only the pTrc99A plasmid exhibited less than 0.001 units/mg of acetohydroxy acid reductoisomerase activity.
The purpose of this Example was to clone the ilvD gene from E. coli K12 and express it in E. coli Top10. The ilvD gene was amplified from E. coli K12 strain FM5 (ATCC 53911) genomic DNA using PCR.
The ilvD gene was cloned and expressed in a similar manner as the ilvC gene described in Example 14. PCR was used to amplify ilvD from the E. coli FM5 genome using primers N114.2 and N115.2 (SEQ ID NOs:35 and 36, respectively). The primers created SacI and NheI sites and an optimal RBS at the 5′ end and Bsu36I, PacI and BamHI sites at the 3′ end of ilvD. The 1.9 kbp PCR product was cloned into pCR4Blunt TOPO according to the manufacturer's protocol (Invitrogen) generating pCR4Blunt TOPO::ilvD. The sequence of the PCR product was confirmed (sequencing primers N132SeqF1-F4 and N132SeqR1-R4, given as SEQ ID NOs:54-61, respectively). To create an expression clone, the ilvD gene was excised from plasmid pCR4Blunt TOPO::ilvD using SacI and BamHI, and cloned into pTrc99A. The pTrc99A::ilvD vector was transformed into E. coli TOP10 cells and expression from the Trc promoter was induced by addition of IPTG, as described in Example 13. Cell-free extracts were prepared as described in Example 5.
Acetohydroxy acid dehydratase activity in the cell free extracts was measured as described in Example 7. Three hours after induction with IPTG, an acetohydroxy acid dehydratase activity of 46 units/mg was measured. The control strain carrying only the pTrc99A plasmid exhibited no detectable acetohydroxy acid dehydratase activity.
The purpose of this Example was to clone the kivD gene from Lactococcus lactis and express it in E. coli TOP10.
The kivD gene was cloned and expressed in a similar manner as that described for ilvC in Example 14 above. PCR was used to amplify kivD from the plasmid pUC57-kivD (see Example 8, above) using primers N116.2 and N117.2 (SEQ ID NOs:37 and 38, respectively). The primers created SacI and PacI sites and an optimal RBS at the 5′ end and PciI, AvrII, BglII and BamHI sites at the 3′ end of kivD. The 1.7 kbp PCR product was cloned into pCR4Blunt TOPO according to the manufacturer's protocol (Invitrogen) generating pCR4Blunt TOPO::kivD. The sequence of the PCR product was confirmed using primers N133SeqF1-F4 and N133SeqR1-R4 (given as SEQ ID NOs:62-69, respectively). To create an expression clone, the kivD gene was excised from plasmid pCR4Blunt TOPO::kivD using SacI and BamHI, and cloned into pTrc99A. The pTrc99A::kivD vector was transformed into E. coli TOP10 cells and expression from the Trc promoter was induced by addition of IPTG, as described in Example 13. Cell-free extracts were prepared as described in Example 5.
Branched-chain keto acid decarboxylase activity in the cell free extracts was measured as described in Example 8, except that Purpald® reagent (Aldrich, Catalog No. 162892) was used to detect and quantify the aldehyde reaction products. Three hours after induction with IPTG, a branched-chain keto acid decarboxylase activity of greater than 3.7 units/mg was detected. The control strain carrying only the pTrc99A plasmid exhibited no detectable branched-chain keto acid decarboxylase activity.
E. coli contains a native gene (yqhD) that was identified as a 1,3-propanediol dehydrogenase (U.S. Pat. No. 6,514,733). The YqhD protein has 40% identity to AdhB (encoded by adhB) from Clostridium, a putative NADH-dependent butanol dehydrogenase. The yqhD gene was placed under the constitutive expression of a variant of the glucose isomerase promoter 1.6GI (SEQ ID NO. 70) in E. coli strain MG1655 1.6yqhD::Cm (WO 2004/033646) using λ Red technology (Datsenko and Wanner, Proc. Natl. Acad. Sci. U.S.A. 97:6640 (2000)). MG1655 1.6yqhD::Cm contains a FRT-CmR-FRT cassette so that the antibiotic marker can be removed. Similarly, the native promoter was replaced by the 1.5GI promoter (WO 2003/089621) (SEQ ID NO. 71), creating strain MG1655 1.5GI-yqhD::Cm, thus, replacing the 1.6GI promoter of MG1655 1.6yqhD::Cm with the 1.5GI promoter.
Strain MG1655 1.5GI-yqhD::Cm was grown in LB medium to mid-log phase and cell free extracts were prepared as described in Example 5. This strain was found to have NADPH-dependent isobutyraldehyde reductase activity when the cell extracts were assayed by following the decrease in absorbance at 340 nm at pH 7.5 and 35° C.
To generate a second expression strain containing 1.5GI yqhD::Cm, a P1 lysate was prepared from MG1655 1.5GI yqhD::Cm and the cassette was transferred to BL21 (DE3) (Invitrogen) by transduction, creating BL21 (DE3) 1.5GI-yqhD::Cm.
The purpose of this Example was to construct a transformation vector comprising the first four genes (i.e., budB, ilvC, ilvD and kivD) in an isobutanol biosynthetic pathway.
To construct the transformation vector, first, the ilvC gene was obtained from pTrc99A::ilvC (described in Example 14) by digestion with AflII and BamHI and cloned into pTrc99A::budB (described in Example 13), which was digested with AflII and BamHI to produce plasmid pTrc99A::budB-ilvC. Next, the ilvD and kivD genes were obtained from pTrc99A::ilvD (described in Example 15) and pTrc99A::kivD (described in Example 16), respectively, by digestion with NheI and PacI (ilvD) and PacI and BamHI (kivD). These genes were introduced into pTrc99A::budB-ilvC, which was first digested with NheI and BamHI, by three-way ligation. The presence of all four genes in the final plasmid, pTrc99A::budB-ilvC-ilvD-kivD, was confirmed by PCR screening and restriction digestion.
To create E. coli isobutanol production strains, pTrc99A::budB-ilvC-ilvD-kivD (described in Example 18) was transformed into E. coli MG1655 1.5GI yqhD::Cm and E. coli BL21 (DE3) 1.5GI yqhD::Cm (described in Example 17). Transformants were initially grown in LB medium containing 50 μg/mL kanamycin and 100 μg/mL carbenicillin. The cells from these cultures were used to inoculate shake flasks (approximately 175 mL total volume) containing 50 or 170 mL of TM3a/glucose medium (with appropriate antibiotics) to represent high and low oxygen conditions, respectively. TM3a/glucose medium contained (per liter): glucose (10 g), KH2PO4 (13.6 g), citric acid monohydrate (2.0 g), (NH4)2SO4 (3.0 g), MgSO4.7H2O (2.0 g), CaCl2.2H2O (0.2 g), ferric ammonium citrate (0.33 g), thiamine.HCl (1.0 mg), yeast extract (0.50 g), and 10 mL of trace elements solution. The pH was adjusted to 6.8 with NH4OH. The trace elements solution contained: citric acid H2O (4.0 g/L), MnSO4.H2O (3.0 g/L), NaCl (1.0 g/L), FeSO4.7H2O (0.10 g/L), COCl2.6H2O (0.10 g/L), ZnSO4.7H2O (0.10 g/L), CuSO4.5H2O (0.010 g/L), H3BO3 (0.010 g/L), and Na2MoO4.2H2O (0.010 g/L).
The flasks were inoculated at a starting OD600 of <0.01 units and incubated at 34° C. with shaking at 300 rpm. The flasks containing 50 mL of medium were closed with 0.2 μm filter caps; the flasks containing 150 mL of medium were closed with sealed caps. IPTG was added to a final concentration of 0.04 mM when the cells reached an OD600 of >0.4 units. Approximately 18 h after induction, an aliquot of the broth was analyzed by HPLC (Shodex Sugar SH1011 column (Showa Denko America, Inc. NY) with refractive index (RI) detection) and GC (Varian CP-WAX 58(FFAP) CB, 0.25 mm×0.2 μm×25 m (Varian, Inc., Palo Alto, Calif.) with flame ionization detection (FID)) for isobutanol content, as described in the General Methods section. No isobutanol was detected in control strains carrying only the pTrc99A vector (results not shown). Molar selectivities and titers of isobutanol produced by strains carrying pTrc99A::budB-ilvC-ilvD-kivD are shown in Table 13. Significantly higher titers of isobutanol were obtained in the cultures grown under low oxygen conditions.
Since the strains described in Example 19 were not capable of growth on sucrose, an additional plasmid was constructed to allow utilization of sucrose for isobutanol production. A sucrose utilization gene cluster cscBKA, given as SEQ ID NO:39, was isolated from genomic DNA of a sucrose-utilizing E. coli strain derived from ATCC strain 13281. The sucrose utilization genes (cscA, cscK, and cscB) encode a sucrose hydrolase (CscA), given as SEQ ID NO:139, D-fructokinase (CscK), given as SEQ ID NO:140, and sucrose permease (CscB), given as SEQ ID NO:141. The sucrose-specific repressorgene cscR was not included so that the three genes cscBKA were expressed constitutively from their native promoters in E. coli.
Genomic DNA from the sucrose-utilizing E. coli strain was digested to completion with BamHI and EcoRI. Fragments having an average size of about 4 kbp were isolated from an agarose gel and were ligated to plasmid pLitmus28 (New England Biolabs), digested with BamHI and EcoRI and transformed into ultracompetent E. coli TOP10F′ cells (Invitrogen). The transformants were streaked onto MacConkey agar plates containing 1% sucrose and ampicillin (100 μg/mL) and screened for the appearance of purple colonies. Plasmid DNA was isolated from the purple transformants, and sequenced with M13 Forward and Reverse primers (Invitrogen), and Scr1-4 (given as SEQ ID NOs:72-75, respectively). The plasmid containing cscB, csck, and cscA (cscBKA) genes was designated pScr1.
To create a sucrose utilization plasmid that was compatible with the isobutanol pathway plasmid (Example 18), the operon from pScr1 was subcloned into pBHR1 (MoBiTec, Goettingen, Germany). The cscBKA genes were isolated by digestion of pScr1 with XhoI (followed by incubation with Klenow enzyme to generate blunt ends) and then by digestion with AgeI. The resulting 4.2 kbp fragment was ligated into pBHR1 that had been digested with NaeI and AgeI, resulting in the 9.3 kbp plasmid pBHR1::cscBKA.
The sucrose plasmid pBHR1::cscBKA was transformed into E. coli BL21 (DE3) 1.5 yqhD/pTrc99A::budB-ilvC-ilvD-kivD and E. coli MG1655 1.5yqhD/pTrc99A::budB-ilvC-ilvD-kivD (described in Example 19) by electroporation. Transformants were first selected on LB medium containing 100 μg/mL ampicillin and 50 μg/mL kanamycin and then screened on MacConkey sucrose (1%) plates to confirm functional expression of the sucrose operon. For production of isobutanol, strains were grown in TM3a minimal defined medium (described in Example 19) containing 1% sucrose instead of glucose, and the culture medium was analyzed for the amount of isobutanol produced, as described in Example 19, except that samples were taken 14 h after induction. Again, no isobutanol was detected in control strains carrying only the pTrc99A vector (results not shown). Molar selectivities and titers of isobutanol produced by MG1655 1.5yqhD carrying pTrc99A::budB-ilvC-ilvD-kivD are shown in Table 14. Similar results were obtained with the analogous BL21 (DE3) strain.
To express isobutanol pathway genes in Saccharomyces cerevisiae, a number of E. coli-yeast shuttle vectors were constructed. A PCR approach (Yu, et al. Fungal Genet. Biol. 41:973-981 (2004)) was used to fuse genes with yeast promoters and terminators. Specifically, the GPD promoter (SEQ ID NO:76) and CYC1 terminator (SEQ ID NO:77) were fused to the alsS gene from Bacillus subtilis (SEQ ID NO:78), the FBA promoter (SEQ ID NO:79) and CYC1 terminator were fused to the ILV5 gene from S. cerevisiae (SEQ ID NO:80), the ADH1 promoter (SEQ ID NO:81) and ADH1 terminator (SEQ ID NO:82) were fused to the ILV3 gene from S. cerevisiae (SEQ ID NO:83), and the GPM promoter (SEQ ID NO:84) and ADH1 terminator were fused to the kivD gene from Lactococcus lactis (SEQ ID NO:7). The primers, given in Table 15, were designed to include restriction sites for cloning promoter/gene/terminator products into E. coli-yeast shuttle vectors from the pRS400 series (Christianson et al. Gene 110:119-122 (1992)) and for exchanging promoters between constructs. Primers for the 5′ ends of ILV5 and ILV3 (N138 and N155, respectively, given as SEQ ID NOs: 95 and 107, respectively) generated new start codons to eliminate mitochondrial targeting of these enzymes.
All fused PCR products were first cloned into pCR4-Blunt by TOPO cloning reaction (Invitrogen) and the sequences were confirmed (using M13 forward and reverse primers (Invitrogen) and the sequencing primers provided in Table 15. Two additional promoters (CUP1 and GALL) were cloned by TOPO reaction into pCR4-Blunt and confirmed by sequencing; primer sequences are indicated in Table 15. The plasmids that were constructed are described in Table 16. The plasmids were transformed into either Saccharomyces cerevisiae BY4743 (ATCC 201390) or YJR148w (ATCC 4036939) to assess enzyme specific activities using the enzyme assays described in Examples 5-8 and Examples 13-16. For the determination of enzyme activities, cultures were grown to an OD600 of 1.0 in synthetic complete medium (Methods in Yeast Genetics, 2005, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., pp. 201-202) lacking any metabolite(s) necessary for selection of the expression plasmid(s), harvested by centrifugation (2600×g for 8 min at 4° C.), washed with buffer, centrifuged again, and frozen at −80° C. The cells were thawed, resuspended in 20 mM Tris-HCl, pH 8.0 to a final volume of 2 mL, and then disrupted using a bead beater with 1.2 g of glass beads (0.5 mm size). Each sample was processed on high speed for 3 minutes total (with incubation on ice after each minute of beating). Extracts were cleared of cell debris by centrifugation (20,000×g for 10 min at 4° C.).
S. cerevisiae Expression Vectors
B. subtilis alsS
B. subtilis alsS
B. subtilis alsS
B. subtilis alsS
B. subtilis alsS
B. subtilis alsS
B. subtilis alsS
B. subtilis alsS
E. coli-Yeast Shuttle Vectors Carrying Isobutanol Pathway Genes
Plasmids pRS423::CUP1-alsS+FBA-ILV3 and pHR81::FBA-ILV5+GPM-kivD (described in Example 21) were transformed into Saccharomyces cerevisiae YJR148w to produce strain YJR148w/pRS423::CUP1-alsS+FBA-ILV3/pHR81::FBA-ILV5+ GPM-kivD. A control strain was prepared by transforming vectors pRS423 and pHR81 (described in Example 21) into Saccharomyces cerevisiae YJR148w (strain YJR148w/pRS423/pHR81). Strains were maintained on standard S. cerevisiae synthetic complete medium (Methods in Yeast Genetics, 2005, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., pp. 201-202) containing either 2% glucose or sucrose but lacking uracil and histidine to ensure maintenance of plasmids.
For isobutanol production, cells were transferred to synthetic complete medium lacking uracil, histidine and leucine. Removal of leucine from the medium was intended to trigger an increase in copy number of the pHR81-based plasmid due to poor transcription of the leu2-d allele (Erhart and Hollenberg, J. Bacteriol. 156:625-635 (1983)). Aerobic cultures were grown in 175 mL capacity flasks containing 50 mL of medium in an Innova4000 incubator (New Brunswick Scientific, Edison, N.J.) at 30° C. and 200 rpm. Low oxygen cultures were prepared by adding 45 mL of medium to 60 mL serum vials that were sealed with crimped caps after inoculation and kept at 30° C. Sterile syringes were used for sampling and addition of inducer, as needed. Approximately 24 h after inoculation, the inducer CuSO4 was added to a final concentration of 0.03 mM. Control cultures for each strain without CuSO4 addition were also prepared. Culture supernatants were analyzed 18 or 19 h and 35 h after CuSO4 addition by both GC and HPLC for isobutanol content, as described above in Example 19. The results for S. cerevisiae YJR148w/pRS423::CUP1-alsS+FBA-ILV3/pHR81::FBA-ILV5+GPM-kivD grown on glucose are presented in Table 17. For the results given in Table 17, the samples from the aerobic cultures were taken at 35 h and the samples from the low oxygen cultures were taken at 19 h and measured by HPLC.
The results for S. cerevisiae YJR148w/pRS423::CUP1-alsS+FBA-ILV3/pHR81::FBA-ILV5+GPM-kivD grown on sucrose are presented in Table 18. The results in this table were obtained with samples taken at 18 h and measured by HPLC.
The results indicate that, when grown on glucose or sucrose under both aerobic and low oxygen conditions, strain YJR148w/pRS423::CUP1-alsS+FBA-ILV3/pHR81::FBA-ILV5+GPM-kivD produced consistently higher levels of isobutanol than the control strain.
Plasmids pRS425::CUP1-alsS+FBA-ILV3 and pRS426::GAL1-ILV5+GPM-kivD (described in Example 21) were transformed into Saccharomyces cerevisiae YJR148w to produce strain YJR148w/pRS425::CUP1-alsS+FBA-ILV3/pRS426::GAL1-ILV5+GPM-kivD. A control strain was prepared by transforming vectors pRS425 and pRS426 (described in Example 21) into Saccharomyces cerevisiae YJR148w (strain YJR148w/pRS425/pRS426). Strains were maintained on synthetic complete medium, as described in Example 22.
For isobutanol production, cells were transferred to synthetic complete medium containing 2% galactose and 1% raffinose, and lacking uracil and leucine. Aerobic and low oxygen cultures were prepared as described in Example 22. Approximately 12 h after inoculation, the inducer CuSO4 was added up to a final concentration of 0.5 mM. Control cultures for each strain without CuSO4 addition were also prepared. Culture supernatants were sampled 23 h after CuSO4 addition for determination of isobutanol by HPLC, as described in Example 22. The results are presented in Table 19. Due to the widely different final optical densities observed and associated with quantifying the residual carbon source, the concentration of isobutanol per OD600 unit (instead of molar selectivities) is provided in the table to allow comparison of strains containing the isobutanol biosynthetic pathway genes with the controls.
The results indicate that in general, higher levels of isobutanol per optical density unit were produced by the YJR148w/pRS425::CUP1-alsS+FBA-ILV3/pRS426::GAL1-ILV5+GPM-kivD strain compared to the control strain under both aerobic and low oxygen conditions.
The purpose of this Example was to express an isobutanol biosynthetic pathway in Bacillus subtilis. The five genes of the isobutanol pathway (pathway steps (a) through (e) in
Integration of the three genes, budB, ilvD and kivD into the chromosome of B. subtilis BE1010. Bacillus integration vectors pFP988DssPspac and pFP988DssPgroE were used for the chromosomal integration of the three genes, budB (SEQ ID NO:1), ilvD (SEQ ID NO:5), and kivD (SEQ ID NO:7). Both plasmids contain an E. coli replicon from pBR322, an ampicillin antibiotic marker for selection in E. coli and two sections of homology to the sacB gene in the Bacillus chromosome that direct integration of the vector and intervening sequence by homologous recombination. Between the sacB homology regions is a spac promoter (PgroE) on pFP988DssPspac or a groEL promoter (PgroE) on pFP988DssPgroE, and a selectable marker for Bacillus, erythromycin. The promoter region also contains the lacO sequence for regulation of expression by a lacI repressor protein. The sequences of pFP988DssPspac (6,341 bp) and pFP988DssPgroE (6,221 bp) are given as SEQ ID NO:142 and SEQ ID NO:143 respectively.
The cassette with three genes budB-ilvD-kivD was constructed by deleting the ilvC gene from plasmid pTrc99a budB-ilvC-ilvD-kivD. The construction of the plasmid pTrc99A::budB-ilvC-ilvD-kivD is described in Example 18. Plasmid pTrc99A::budB-ilvC-ilvD-kivD was digested with AflII and NheI, treated with the Klenow fragment of DNA polymerase to make blunt ends, and the resulting 9.4 kbp fragment containing pTrc99a vector, budB, ilvD, and kivD was gel-purified. The 9.4 kbp vector fragment was self-ligated to create pTrc99A::budB-ilvD-kivD, and transformed into DH5α competent cells (Invitrogen). A clone of pTrc99a budB-ilvD-kivD was confirmed for the ilvC gene deletion by restriction mapping. The resulting plasmid pTrc99A::budB-ilvD-kivD was digested with SacI and treated with the Klenow fragment of DNA polymerase to make blunt ends. The plasmid was then digested with BamHI and the resulting 5,297 bp budB-ilvD-kivD fragment was gel-purified. The 5,297 bp budB-ilvD-kivD fragment was ligated into the SmaI and BamHI sites of the integration vector pFP988DssPspac. The ligation mixture was transformed into DH5α competent cells. Transformants were screened by PCR amplification of the 5.3 kbp budB-ilvD-kivD fragment with primers T-budB(BamHI) (SEQ ID NO:144) and B-kivD(BamHI) (SEQ ID NO:145). The correct clone was named pFP988DssPspac-budB-ilvD-kivD.
Plasmid pFP988DssPspac-budB-ilvD-kivD was prepared from the E. coli transformant, and transformed into B. subtilis BE1010 competent cells, which had been prepared as described by Doyle et al. (J. Bacteriol. 144:957 (1980)). Competent cells were harvested by centrifugation and the cell pellets were resuspended in a small volume of the supernatant. To one volume of competent cells, two volumes of SPII-EGTA medium (Methods for General and Molecular Bacteriology, P. Gerhardt et al., Ed., American Society for Microbiology, Washington, D.C. (1994)) was added. Aliquots (0.3 mL) of cells were dispensed into test tubes and then 2 to 3 μg of plasmid pFP988DssPspac-budB-ilvD-kivD was added to the tubes. The tubes were incubated for 30 min at 37° C. with shaking, after which 0.1 mL of 10% yeast extract was added to each tube and they were further incubated for 60 min. Transformants were grown for selection on LB plates containing erythromycin (1.0 μg/mL) using the double agar overlay method (Methods for General and Molecular Bacteriology, supra). Transformants were screened by PCR amplification with primers N130SeqF1 (SEQ ID NO:40) and N130SeqR1 (SEQ ID NO:44) for budB, and N133SeqF1 (SEQ ID NO:62) and N133SeqR1 (SEQ ID NO:66) for kivD. Positive integrants showed the expected 1.7 kbp budB and 1.7 kbp kivD PCR products. Two positive integrants were identified and named B. subtilis BE1010 ΔsacB::Pspac-budB-ilvD-kivD #2-3-2 and B. subtilis BE1010 ΔsacB::Pspac-budB-ilvD-kivD #6-12-7.
Assay of the enzyme activities in integrants B. subtilis BE1010 ΔsacB::Pspac-budB-ilvD-kivD #2-3-2 and B. subtilis BE1010 ΔsacB::Pspac-budB-ilvD-kivD #6-12-7 indicated that the activities of BudB, IlvD and KivD were low under the control of the spac promoter (Pspac). To improve expression of functional enzymes, the Pspac promoter was replaced by a PgroE promoter from plasmid pHT01 (MoBitec, Goettingen, Germany).
A 6,039 bp pFP988Dss vector fragment, given as SEQ ID NO:146, was excised from an unrelated plasmid by restriction digestion with XhoI and BamHI, and was gel-purified. The PgroE promoter was PCR-amplified from plasmid pHT01 with primers T-groE(XhoI) (SEQ ID NO:147) and B-groEL(SpeI,BamH1) (SEQ ID NO:148). The PCR product was digested with XhoI and BamHI, ligated with the 6,039 bp pFP988Dss vector fragment, and transformed into DH5α competent cells. Transformants were screened by PCR amplification with primers T-groE(XhoI) and B-groEL(SpeI,BamH1). Positive clones showed the expected 174 bp PgroE PCR product and were named pFP988DssPgroE. The plasmid pFP988DssPgroE was also confirmed by DNA sequence.
Plasmid pFP988DssPspac-budB-ilvD-kivD was digested with SpeI and PmeI and the resulting 5,313 bp budB-ilvD-kivD fragment was gel-purified. The budB-ilvD-kivD fragment was ligated into SpeI and PmeI sites of pFP988DssPgroE and transformed into DH5α competent cells. Positive clones were screened for a 1,690 bp PCR product by PCR amplification with primers T-groEL (SEQ ID NO:149) and N111 (SEQ ID NO:20). The positive clone was named pFP988DssPgroE-budB-ilvD-kivD.
Plasmid pFP988DssPgroE-budB-ilvD-kivD was prepared from the E. coli transformant, and transformed into Bacillus subtilis BE1010 competent cells as described above. Transformants were screened by PCR amplification with primers N130SeqF1 (SEQ ID NO:40) and N130SeqR1 (SEQ ID NO:44) for budB, and N133SeqF1 (SEQ ID NO:62) and N133SeqR1 (SEQ ID NO:66) for kivD. Positive integrants showed the expected 1.7 kbp budB and 1.7 kbp kivD PCR products. Two positive integrants were isolated and named B. subtilis BE1010 ΔsacB::PgroE-budB-ilvD-kivD #1-7 and B. subtilis BE1010 ΔsacB::PgroE-budB-ilvD-kivD #8-16.
Plasmid Expression of ilvC and bdhB genes. Two remaining isobutanol genes, ilvC and bdhB, were expressed from a plasmid. Plasmid pHT01 (MoBitec), a Bacillus-E. coli shuttle vector, was used to fuse an ilvC gene from B. subtilis to a PgroE promoter so that the ilvC gene was expressed from the PgroE promoter containing a lacO sequence. The ilvC gene, given as SEQ ID NO:186, was PCR-amplified from B. subtilis BR151 (ATCC 33677) genomic DNA with primers T-ilvCB.s.(BamHI) (SEQ ID NO:150) and B-ilvCB.s.(SpeI BamHI) (SEQ ID NO:151). The 1,067 bp ilvC PCR product was digested with BamHI and ligated into the BamHI site of pHT01. The ligation mixture was transformed into DH5α competent cells. Positive clones were screened for a 1,188 bp PCR product by PCR amplification with primers T-groEL and B-ilvB.s.(SpeI BamHI). The positive clone was named pHT01-ilvC(B.s). Plasmid pHT01-ilvC(B.s) was used as a template for PCR amplification of the PgroE-ilvC fused fragment.
Plasmid pBD64 (Minton et al., Nucleic Acids Res. 18:1651 (1990)) is a fairly stable vector for expression of foreign genes in B. subtilis and contains a repB gene and chloramphenicol and kanamycin resistance genes for selection in B. subtilis. This plasmid was used for expression of ilvC and bdhB under the control of a PgroE promoter. To clone PgroE-ilvC, bdhB and a lacI repressor gene into plasmid pBD64, a one-step assembly method was used (Tsuge et al., Nucleic Acids Res. 31:e133 (2003)). A 3,588 bp pBD64 fragment containing a repB gene, which included the replication function, and the kanamycin antibiotic marker was PCR-amplified from pBD64 with primers T-BD64(DraIII) (SEQ ID NO:152), which introduced a DraIII sequence (CACCGAGTG), and B-BD64(DraIII) (SEQ ID NO:153), which introduced a DraIII sequence (CACCTGGTG). A 1,327 bp lacI repressor gene was PCR-amplified from pMUTIN4 (Vagner et al., Microbiol. 144:3097-3104 (1998)) with T-lacIq(DraIII) (SEQ ID NO:154), which introduced a DraIII sequence (CACCAGGTG) and B-lacIq(DraIII) (SEQ ID NO:155), which introduced a DraIII sequence (CACGGGGTG). A 1,224 bp PgroE-ilvC fused cassette was PCR-amplified from pHT01-ilvC(B.s) with T-groE(DraIII) (SEQ ID NO:156), which introduced a DraIII sequence (CACCCCGTG), and B-B.s.ilvC(DraIII) (SEQ ID NO:157), which introduced a DraIII sequence (CACCGTGTG). A 1.2 kbp bdhB gene (SEQ ID NO:158) was PCR-amplified from Clostridium acetobutylicum (ATCC 824) genomic DNA with primers T-bdhB(DraIII) (SEQ ID NO:159), which introduced a DraIII sequence (CACACGGTG), and B-bdhB(rrnBT1DraIII) (SEQ ID NO:160), which introduced a DraIII sequence (CACTCGGTG). The three underlined letters in the variable region of the DraIII recognition sequences were designed for specific base-pairing to assemble the four fragments with an order of pBD64-lacI-PgroEilvC-bdhB. Each PCR product with DraIII sites at both ends was digested separately with DraIII, and the resulting DraIII fragments, 3,588 bp pBD64, lacI, PgroEilvC, and bdhB were gel-purified using a QIAGEN gel extraction kit (QIAGEN). A mixture containing an equimolar concentration of each fragment with a total DNA concentration of 30 to 50 μg/100 μL was prepared for ligation. The ligation solution was then incubated at 16° C. overnight. The ligation generated high molecular weight tandem repeat DNA. The ligated long, linear DNA mixture was directly transformed into competent B. subtilis BE1010, prepared as described above. B. subtilis preferentially takes up long repeated linear DNA forms, rather than circular DNA to establish a plasmid. After transformation the culture was spread onto an LB plate containing 10 μg/mL of kanamycin for selection. Positive recombinant plasmids were screened by DraIII digestion, giving four fragments with an expected size of 3,588 bp (pBD64), 1,327 bp (lacI), 1,224 bp (PgorE-ilvC), and 1,194 bp (bdhB). The positive plasmid was named pBDPgroE-ilvC(B.s.)-bdhB.
Demonstration of isobutanol production from glucose or sucrose by B. subtilis BE1010 ΔsacB::PgroE-budB-ilvD-kivD/IBDPgroE-ilvC(B.s.)-bdhB. To construct the recombinant B. subtilis expressing the five genes of the isobutanol biosynthetic pathway, competent cells of the two integrants B. subtilis BE1010 ΔsacB-PgroE-budB-ilvD-kivD #1-7 and B. subtilis BE1010 ΔsacB::PgroE-budB-ilvD-kivD #8-16 were prepared as described above, and transformed with plasmid pBDPgroE-ilvC(B.s.)-bdhB, yielding B. subtilis BE1010 ΔsacB::PgroE-budB-ilvD-kivD #1-7/pBDPgroE-ilvC(B.s.)-bdhB and B. subtilis BE1010 ΔsacB::PgroE-budB-ilvD-kivD #8-16/pBDPgroE-ilvC(B.s.)-bdhB.
The two recombinant strains were inoculated in either 25 mL or 100 mL of glucose medium containing kanamycin (10 μg/mL) in 125 mL flasks to simulate high and low oxygen conditions, respectively, and aerobically grown at 37° C. with shaking at 200 rpm. The medium consisted of 10 mM (NH4)2SO4, 5 mM potassium phosphate buffer (pH 7.0), 100 mM MOPS/KOH buffer (pH 7.0), 20 mM glutamic acid/KOH (pH 7.0), 2% S10 metal mix, 1% glucose, 0.01% yeast extract, 0.01% casamino acids, and 50 μg/mL each of L-tryptophan, L-methionine, and L-lysine. The S10 metal mix consisted of 200 mM MgCl2, 70 mM CaCl2, 5 mM MnCl2, 0.1 mM FeCl3, 0.1 mM ZnCl2, 0.2 mM thiamine hydrochloride, 0.172 mM CuSO4, 0.253 mM COCl2, and 0.242 mM Na2MoO4. The cells were induced with 1.0 mM isopropyl-β-D-thiogalactopyranoiside (IPTG) at early-log phase (OD600 of approximately 0.2). At 24 h after inoculation, an aliquot of the broth was analyzed by HPLC (Shodex Sugar SH1011 column) with refractive index (R1) detection for isobutanol content, as described in the General Methods section. The HPLC results are shown in Table 20.
B. subtilis a
B. subtilis b
B. subtilis a
B. subtilis b
B. subtilis a is B. subtilis BE1010 ΔsacB::PgroE-budB-ilvD-kivD #1-7/pBDPgroE-ilvC(B.s.)-bdhB
B. subtilis b is B. subtilis BE1010 ΔsacB::PgroE-budB-ilvD-kivD #8-16/pBDPgroE-ilvC(B.s.)-bdhB
The isolate of B. subtilis BE1010 ΔsacB::PgroE-budB-ilvD-kivD #1-7/pBDPgroE-ilvC(B.s.)-bdhB was also examined for isobutanol production from sucrose, essentially as described above. The recombinant strain was inoculated in 25 mL or 75 mL of sucrose medium containing kanamycin (10 μg/mL) in 125 mL flasks to simulate high and medium oxygen levels, and grown at 37° C. with shaking at 200 rpm. The sucrose medium was identical to the glucose medium except that glucose (10 g/L) was replaced with 10 g/L of sucrose. The cells were uninduced, or induced with 1.0 mM isopropyl-β-D-thiogalactopyranoiside (IPTG) at early-log phase (OD600 of approximately 0.2). At 24 h after inoculation, an aliquot of the broth was analyzed by HPLC (Shodex Sugar SH1011 column) with refractive index (RI) detection for isobutanol content, as described in the General Methods section. The HPLC results are given in Table 21.
B. subtilis a
B. subtilis a
B. subtilis a
B. subtilis a is B. subtilis BE1010 ΔsacB::PgroE-budB-ilvD-kivD #1-7/pBDPgroE-ilvC(B.s.)-bdhB
The purpose of this prophetic Example is to describe how to express an isobutanol biosynthetic pathway in Lactobacillus plantarum. The five genes of the isobutanol pathway, encoding five enzyme activities, are divided into two operons for expression. The budB, ilvD and kivD genes, encoding the enzymes acetolactate synthase, acetohydroxy acid dehydratase, and branched-chain α-keto acid decarboxylase, respectively, are integrated into the chromosome of Lactobacillus plantarum by homologous recombination using the method described by Hols et al. (Appl. Environ. Microbiol. 60:1401-1413 (1994)). The remaining two genes (ilvC and bdhB, encoding the enzymes acetohydroxy acid reductoisomerase and butanol dehydrogenase, respectively) are cloned into an expression plasmid and transformed into the Lactobacillus strain carrying the integrated isobutanol genes. Lactobacillus plantarum is grown in MRS medium (Difco Laboratories, Detroit, Mich.) at 37° C., and chromosomal DNA is isolated as described by Moreira et al. (BMC Microbiol. 5:15 (2005)).
Integration. The budB-ilvD-kivD cassette under the control of the synthetic P11 promoter (Rud et al., Microbiology 152:1011-1019 (2006)) is integrated into the chromosome of Lactobacillus plantarum ATCC BAA-793 (NCIMB 8826) at the ldhL1 locus by homologous recombination. To build the ldhL integration targeting vector, a DNA fragment from Lactobacillus plantarum (Genbank NC—004567) with homology to ldhL is PCR amplified with primers LDH EcoRV F (SEQ ID NO:161) and LDH AatIIR (SEQ ID NO:162). The 1986 bp PCR fragment is cloned into pCR4Blunt-TOPO and sequenced. The pCR4Blunt-TOPO-ldhL1 clone is digested with EcoRV and AatII releasing a 1982 bp ldhL1 fragment that is gel-purified. The integration vector pFP988, given as SEQ ID NO:177, is digested with HindIII and treated with Klenow DNA polymerase to blunt the ends. The linearized plasmid is then digested with AatII and the 2931 bp vector fragment is gel purified. The EcoRV/AatII ldhL1 fragment is ligated with the pFP988 vector fragment and transformed into E. coli Top10 cells. Transformants are selected on LB agar plates containing ampicillin (100 μg/mL) and are screened by colony PCR to confirm construction of pFP988-ldhL.
To add a selectable marker to the integrating DNA, the Cm gene with its promoter is PCR amplified from pC194 (GenBank NC—002013, SEQ ID NO:267) with primers Cm F (SEQ ID NO:163) and Cm R (SEQ ID NO:164), amplifying a 836 bp PCR product. This PCR product is cloned into pCR4Blunt-TOPO and transformed into E. coli Top10 cells, creating pCR4Blunt-TOPO-Cm. After sequencing to confirm that no errors are introduced by PCR, the Cm cassette is digested from pCR4Blunt-TOPO-Cm as an 828 bp MluI/SwaI fragment and is gel purified. The ldhL-homology containing integration vector pFP988-ldhL is digested with MluI and SwaI and the 4740 bp vector fragment is gel purified. The Cm cassette fragment is ligated with the pFP988-ldhL vector creating pFP988-DldhL::Cm.
Finally the budB-ilvD-kivD cassette from pFP988DssPspac-budB-ilvD-kivD, described in Example 24, is modified to replace the amylase promoter with the synthetic P11 promoter. Then, the whole operon is moved into pFP988-DldhL::Cm. The P11 promoter is built by oligonucleotide annealing with primer P11 F-StuI (SEQ ID NO:165) and P11 R-SpeI (SEQ ID NO: 166). The annealed oligonucleotide is gel-purified on a 6% Ultra PAGE gel (Embi Tec, San Diego, Calif.). The plasmid pFP988DssPspac-budB-ilvD-kivD, containing the amylase promoter, is digested with StuI and SpeI and the resulting 10.9 kbp vector fragment is gel-purified. The isolated P11 fragment is ligated with the digested pFP988DssPspac-budB-ilvD-kivD to create pFP988-P11-budB-ilvD-kivD. Plasmid pFP988-P11-budB-ilvD-kivD is then digested with StuI and BamHI and the resulting 5.4 kbp P11-budB-ilvD-kivD fragment is gel-purified. pFP988-DldhL::Cm is digested with HpaI and BamHI and the 5.5 kbp vector fragment isolated. The budB-ilvD-kivD operon is ligated with the integration vector pFP988-DldhL::Cm to create pFP988-DldhL-P11-budB-ilvD-kivD::Cm.
Integration of pFP988-DldhL-P11-budB-ilvD-kivD::Cm into L. plantarum BAA-793 to form L. plantarum AldhL1::budB-ilvD-kivD::Cm comprising exogenous budB. ilvD, and kivD genes. Electrocompetent cells of L. plantarum are prepared as described by Aukrust, T. W., et al. (In: Electroporation Protocols for Microorganisms; Nickoloff, J. A., Ed.; Methods in Molecular Biology, Vol. 47; Humana Press, Inc., Totowa, N.J., 1995, pp 201-208). After electroporation, cells are outgrown in MRSSM medium (MRS medium supplemented with 0.5 M sucrose and 0.1 M MgCl2) as described by Aukrust et al. supra for 2 h at 37° C. without shaking. Electroporated cells are plated for selection on MRS plates containing chloramphenicol (10 μg/mL) and incubated at 37° C. Transformants are initially screened by colony PCR amplification to confirm integration, and initial positive clones are then more rigorously screened by PCR amplification with a battery of primers.
Plasmid Expression of ilvC and bdhB genes. The remaining two isobutanol genes are expressed from plasmid pTRKH3 (O'Sullivan D J and Klaenhammer T R, Gene 137:227-231 (1993)) under the control of the L. plantarum ldhL promoter (Ferain et al., J. Bacteriol. 176:596-601 (1994)). The ldhL promoter is PCR amplified from the genome of L. plantarum ATCC BAA-793 using primers PldhL F-HindIII (SEQ ID NO:167) and PldhL R-BamHI (SEQ ID NO:168). The 411 bp PCR product is cloned into pCR4Blunt-TOPO and sequenced. The resulting plasmid, pCR4Blunt-TOPO-PldhL is digested with HindIII and BamHI releasing the PldhL fragment.
Plasmid pTRKH3 is digested with HindIII and SphI and the gel-purified vector fragment is ligated with the PldhL fragment and the gel-purified 2.4 kbp BamHI/SphI fragment containing ilvC(B.s.)-bdhB from the Bacillus expression plasmid pBDPgroE-ilvC(B.s.)-bdhB (Example 24) in a three-way ligation. The ligation mixture is transformed into E. coli Top 10 cells and transformants are grown on Brain Heart Infusion (BHI, Difco Laboratories, Detroit, Mich.) plates containing erythromycin (150 mg/L). Transformants are screened by PCR to confirm construction. The resulting expression plasmid, pTRKH3-ilvC(B.s.)-bdhB is transformed into L. plantarum ΔldhL1::budB-ilvD-kivD::Cm by electroporation, as described above.
L. plantarum ΔldhL1::budB-ilvD-kivD::Cm containing pTRKH3-ilvC(B.s.)-bdhB is inoculated into a 250 mL shake flask containing 50 mL of MRS medium plus erythromycin (10 μg/mL) and grown at 37° C. for 18 to 24 h without shaking, after which isobutanol is detected by HPLC or GC analysis, as described in the General Methods section.
The purpose of this prophetic Example is to describe how to express an isobutanol biosynthetic pathway in Enterococcus faecalis. The complete genome sequence of Enterococcus faecalis strain V583, which is used as the host strain for the expression of the isobutanol biosynthetic pathway in this Example, has been published (Paulsen et al., Science 299:2071-2074 (2003)). An E. coli/Gram-positive shuttle vector, Plasmid pTRKH3 (O'Sullivan D J and Klaenhammer T R, Gene 137:227-231 (1993)), is used for expression of the five genes (budB, ilvC, ilvD, kivD, bdhB) of the isobutanol pathway in one operon. pTRKH3 contains an E. coli plasmid p15A replication origin, the pAMβ1 replicon, and two antibiotic resistance selection markers for tetracycline and erythromycin. Tetracycline resistance is only expressed in E. coli, and erythromycin resistance is expressed in both E. coli and Gram-positive bacteria. Plasmid pAMβ1 derivatives can replicate in E. faecalis (Poyart et al., FEMS Microbiol. Lett. 156:193-198 (1997)). The inducible nisA promoter (PnisA), which has been used for efficient control of gene expression by nisin in a variety of Gram-positive bacteria including Enterococcus faecalis (Eichenbaum et al., Appl. Environ. Microbiol. 64:2763-2769 (1998)), is used to control expression of the five desired genes encoding the enzymes of the isobutanol biosynthetic pathway.
The plasmid pTrc99A::budB-ilvC-ilvD-kivD (described in Example 18), which contains the isobutanol pathway operon, is modified to replace the E. coli ilvC gene (SEQ ID NO:3) with the B. subtilis ilvC gene (SEQ ID NO:184). Additionally, the bdhB gene (SEQ ID NO:158) from Clostridium acetobutylicum is added to the end of the operon. First, the bdhB gene from pBDPgroE-ilvC(B.s.)-bdhB (described in Example 24) is amplified using primers F-bdhB-AvrII (SEQ ID NO:169) and R-bdhB-BamHI (SEQ ID NO:170), and then TOPO cloned and sequenced. The 1194 bp bdhB fragment is isolated by digestion with AvrII and BamHI, followed by gel purification. This bdhB fragment is ligated with pTrc99A::budB-ilvC-ilvD-kivD that has previously been digested with AvrII and BamHI and the resulting fragment is gel purified. The ligation mixture is transformed into E. coli Top10 cells by electroporation and transformants are selected following overnight growth at 37° C. on LB agar plates containing ampicillin (100 μg/mL). The transformants are then screened by colony PCR to confirm the correct clone containing pTrc99A::budB-ilvC-ilvD-kivD-bdhB.
Next, ilvC(B.s.) is amplified from pBDPgroE-ilvC(B.s.)-bdhB (described in Example 24) using primers F-ilvC(B.s.)-AflII (SEQ ID NO:171) and R-ilvC(B.s.)-NotI (SEQ ID NO:172). The PCR product is TOPO cloned and sequenced. The 1051 bp ilvC(B.s.) fragment is isolated by digestion with AflII and NotI followed by gel purification. This fragment is ligated with pTrc99A::budB-ilvC-ilvD-kivD-bdhB that has been cut with AflII and NotI to release the E. coli ilvC (the 10.7 kbp vector band is gel purified prior to ligation with ilvC(B.s.)). The ligation mixture is transformed into E. coli Top10 cells by electroporation and transformants are selected following overnight growth at 37° C. on LB agar plates containing ampicillin (100 μg/mL). The transformants are then screened by colony PCR to confirm the correct clone containing pTrc99A::budB-ilvC(B.s.)-ilvD-kivD-bdhB.
To provide a promoter for the E. coli Gram-positive shuttle vector pTRKH3, the nisA promoter (Chandrapati et al., Mol. Microbiol. 46(2):467-477 (2002)) is PCR-amplified from Lactococcus lactis genomic DNA with primers F-PnisA(HindIII) (SEQ ID NO:173) and R-PnisA(SpeI BamHI) (SEQ ID NO:174) and then TOPO cloned. After sequencing, the 213 bp nisA promoter fragment is isolated by digestion with HindIII and BamHI followed by gel purification. Plasmid pTRKH3 is digested with HindIII and BamHI and the vector fragment is gel-purified. The linearized pTRKH3 is ligated with the PnisA fragment and transformed into E. coli Top10 cells by electroporation. Transformants are selected following overnight growth at 37° C. on LB agar plates containing erythromycin (25 μg/mL). The transformants are then screened by colony PCR to confirm the correct clone of pTRKH3-PnisA.
Plasmid pTRKH3-PnisA is digested with SpeI and BamHI, and the vector is gel-purified. Plasmid pTrc99A::budB-ilvC(B.s)-ilvD-kivD-bdhB, described above, is digested with SpeI and BamHI, and the 7.5 kbp fragment is gel-purified. The 7.5 kbp budB-ilvC(B.s)-ilvD-kivD-bdhB fragment is ligated into the pTRKH3-PnisA vector at the SpeI and BamHI sites. The ligation mixture is transformed into E. coli Top10 cells by electroporation and transformants are selected following overnight growth on LB agar plates containing erythromycin (25 μg/mL) at 37° C. The transformants are then screened by colony PCR. The resulting plasmid is named pTRKH3-PnisA-budB-ilvC(B.s)-ilvD-kivD-bdhB. This plasmid is prepared from the E. coli transformants and transformed into electro-competent E. faecalis V583 cells by electroporation using methods known in the art (Aukrust, T. W., et al. In: Electroporation Protocols for Microorganisms; Nickoloff, J. A., Ed.; Methods in Molecular Biology, Vol. 47; Humana Press, Inc., Totowa, N.J., 1995, pp 217-226), resulting in E. faecalis V583/pTRKH3-PnisA-budB-ilvC(B.s)-ilvD-kivD-bdhB.
The second plasmid containing nisA regulatory genes, nisR and nisK, the add9 spectinomycin resistance gene, and the pSH71 origin of replication is transformed into E. faecalis V583/pTRKH3-PnisA-budB-ilvC(B.s)-ilvD-kivD-bdhB by electroporation. The plasmid containing pSH71 origin of replication is compatible with pAMβ1 derivatives in E. faecalis (Eichenbaum et al., supra). Double drug resistant transformants are selected on LB agar plates containing erythromycin (25 μg/mL) and spectinomycin (100 μg/mL), grown at 37° C.
The resulting E. faecalis strain V583B harboring two plasmids, i.e., an expression plasmid (pTRKH3-PnisA-budB-ilvC(B.s)-ilvD-kivD-bdhB) and a regulatory plasmid (pSH71-nisRK), is inoculated into a 250 mL shake flask containing 50 mL of Todd-Hewitt broth supplemented with yeast extract (0.2%) (Fischetti et al., J. Exp. Med. 161:1384-1401 (1985)), nisin (20 μg/mL) (Eichenbaum et al., supra), erythromycin (25 μg/mL), and spectinomycin (100 μg/mL). The flask is incubated without shaking at 37° C. for 18-24 h, after which time, isobutanol production is measured by HPLC or GC analysis, as described in the General Methods section.
Tolerance levels were determined for yeast strain Saccharomyces cerevisiae BY4741 (ATCC 201388) at 25° C. and 30° C. as follows. The strain was cultured in YPD medium. Overnight cultures in the absence of any test compound were started in 25 mL of YPD medium in 150 mL flasks with incubation at 30° C. or at 25° C. in shaking water baths. The next morning, each overnight culture was diluted into a 500 mL flask containing 300 mL of fresh medium to an initial OD600 of about 0.1. The flasks were incubated in shaking water baths at 30° C. or 25°, using the same temperature as used for each overnight culture. The large cultures were incubated for 3 hours and then were split into flasks in the absence (control) and in the presence of 2% or 3% of isobutanol. Growth was followed by measuring OD600 for six hours after addition of the isobutanol. The ΔOD600 was calculated by subtracting the initial OD600 from the final OD600 at 6 hours. The percent growth inhibition relative to the control culture was calculated as follows: % Growth Inhibition=100−[100(Sample ΔOD600/Control ΔOD600)]. The results are summarized in Table 22 below and indicate that growth of strain BY4741 is less inhibited by 2% isobutanol at 25° C. than by 2% isobutanol at 30° C.
| Number | Date | Country | |
|---|---|---|---|
| 60915467 | May 2007 | US |
